You can always watch reply of the games.

Change player you are watching or pres view all button and u can see what, when and in what order other guy is doing.

While watching if u hold ALT u can see if hes doing any microing and which of your ships hes attacking with which ships.

With trade what is important is trade line. This is shortest connected planets with trade ports on it(you can extend it with SB with trade upgrade) throughout your empire. You can see the longest chain if while zoomed out to see galaxy you hover your mouse over credit income. It is represented by white line and it adds 0.1 per length of trade line to each of your trade ports. So best is to build trade line first then go for additional trade ports on planets.( I've seen reply where JJ - one of best players of sins - had nearly 1000 credits ps of income on map 4v4)

It is important how you colonize (some great tips on these forums) and what u colonize first. Pay attention how skilled players are colonizing planets especially is u get into 5v5 or 4v4 skilled game with eco spots. (u can have 4-5 planets colonized in 5 minutes or less easily. 

For replays you need to go to single player/watch game/change to multi player auto save games and the game on the top is last that you played.

PS Economy is important and so is fleet but the most important thing is microing. That means where u place structures (don't have auto placement on) and how u manage your fleet while in fight (u know about counters I assume).

If not search for counters to ships on this forum. There are some nice charts etc....

And for the end 

You can always ask for advice while playing games. Some skilled players wont help but most will since more better players means better games.

PPS Watch all replays of games that were played against better players than you.

Scout (manually) to determine your expansion path which will most likely become your trade line or part of it.

Try not to back track your fleet once you establish your expansion path. For example, that roid, volcanic or ice that is only connected to your home planet can be colonized by some frigates and a colonizer frigate. Don't waste time sending your Colony Capital ship and then backtracking to expand outwards again.

A colonizer frigate can colonize an asteroid unsupported. Simply drop him in and build a turret right next to the roid in front of the siege frigate (entrenchment/diplomacy only). The turret will destroy the siege frigate before it bombs the roid away due to the turret range.

Planets with only one siege frigate can be colonized with a small fleet (even just scouts) and a colonizer frigate. Simply take out the siege frigate and colonize the planet. You can either build a turret depending on the militia size or come back later to clear them out (note: long range frigates can outrange your turret).

Terrans/Desert with a small/medium defended militia can usually be taken with your Colony Capital ship. I like to have a bomber squadron here and target the siege frigates first and then colonize. I either add a turret or send in backup frigates to help with the mop up.

Terrans/Desert with heavily defended militia can be taken with your Colony Capital ship and light support. To limit losses though adding a Carrier Capital ship works wonders with a bomber load out. In this case a repair bay might be needed to keep the capital ship health from getting too low.

If you have a heavily defended terran that isn't in your expansion path a fun way to colonize is to clear the militia with a star base. Simply send in a scout to occupy the militia (shift click him around the grav well) and then send in your star base constructor. Militia will prioritize the scout over the constructing star base. Once the star base is built the militia sacrifice themselves leaving the planet open to colonization.

Thank you all! This advice has been very useful. So. . . In multi-player games do you guys tend to start with a colonizer capital ship or use the colony frigate? 

This question really depends on map size, number of players and player preference. Starting with a colony capital ship is the best way for increasing the speed of colonization as the anti-matter regeneration is much better than a colony frigate. However, Carrier Capital ships are very popular choices as starting capital ships especially for Vasari since their Capital colonizer has a weak benefit compared to the other races.

Colony frigates are almost always used online to secure border worlds, double colonize while the colony capital ship moves a different way or to capture neutral extractors (advent, tec) or build starbases (vasari).

In 4v4 or 5v5 there are typically roles performed in online: Attacker, Defender/Suicide and Econ. In the econ and defender position it is usually recommended to go with a colony capital ship. The Econ position needs to build a strong economy to feed or build pacts (diplomacy) with other players, the suicide player may need to flee to the center of the map requiring a capital ship to survive the journey and colonize distant planets. The attacker may not benefit from a colony capital ship as they will probably be rushing with a carrier capital or defending against the same strategy.

There are different strats, but most people avoid starting with battleships or support capital ships as they have little upside early game currently compared to a colony or carrier capital ship.

True to a point.

With vasari egg u don't get direct colonization benefits but keep in mind that while you're cleaning planets you gain easy experience on it. I usually go between colonization ability and nano disassembler  which is extremely useful against enemy capital ships and star bases especially if you can get all 3 upgrades. And don't forget lvl 6 upgrade drain planet which makes egg formidable force for raids (while you are fighting somewhere else egg can wreck havoc behind enemy lines).

Main reason why people go for skirantra (sometimes 3 or 4 but mostly 2 before they even build any other ship) is because they are overpowered with scramble bomber. If you come against 3 early in game (3 -10min) be very careful. Keep your caps at the edge of grav well and if necessary run them out. There are very hard to defend against so early in game and usually they come with 2 phase missile research.  

Up to 3v3 (included) random map i would say its safe bet to start with colonizer cap ship as well. With 4v4 or above it depends what role you have in the team (are you fighting are you eco or are you in suicide spot) and how skilled players on other team are. They know how to rush quickly and effectively etc... Again say you need help and someone will probably tell you what to build. 

Even if i decide to build colony cap I always build 1-3 colony frigates as well. Usually 1 jump away there is roid which can be colonized with just colony frigate. How was described above. So i send one there. As you will scout (very important early game) you will see where neutrals and possibly other roids are and that is where rest of colonizers go. Depends on the race as well.

Nobody mentioned this before so...

Even if you don't have am on your colony frigate and it doesn't have shields anymore and perhaps slightly damaged hull you can still jump in roids grav well and colonize that roid.

If you do it right colonizer will colonize roid and survive when you run it. The trick is that while holding shift you set colonizers path tightly around asteroid. When it gets 90am colonize and place turret straight away. Siege frigate is already in range to bomb asteroid so u need to be quick.  You probably won't succeed first time especially if colonizer is damaged but play with it and you will make it going.  

Do you mean planetary upkeep?  Always purchase the first population upgrade immediately, and the vast majority of the time you should buy the second level immediately as well.

just get the first population upgrade, that helps deal with the income drain

Roids are only good to colonize because they need only 1 upgrade before you stop loosing income. So for amount of resources they give (metal , crystal) they are really cheap. And you don't need fleet to colonize them. They also have low health 1k HP without upgrade and only 3 civic slots. They don't give you any money income. But yes you need to grab them quick so u don't need to buy minerals and potentially you can sell them. Now if you are not really struggling with cash sell them to other players rather than for 50% of the value. You might have to wait before they are sold but its worth to wait. 

But real value are deserts or teran planets. First have 190 population and 9 civic slots second have 280 population and I think 6 civic slots(a lot of money income from population and room for labs and trade ports). The best thing about them is you don't need any research to colonize them.

Those 2 are very high value planets so make sure you colonize them and if you can stop enemy from colonizing them. (What i sometimes do if i see planet that needs 2 upgrades before you stop loosing income and is sort of border world I let enemy colonize it while I keep my fleet hidden and when he upgrades planet I go and destroy it. It's safe bet he will do it straight away. That is if i have bigger fleet and rest of galaxy is colonized already or he  comes in just with colonizer cap ship. You don't want to sit on the planet with your fleet. Remember if you don't scout and he does you will probably loose as he can build counter to your fleet.)

And yes buy first 2 upgrades straight away. Wait only if it is very likely that you are going to loose planet. Then if you colonized if need to build repair platforms or/and turrets.

While attacking planet always kill constructor first (4 min without building capabilities) so if you kill repair or factories they stay down. And if you see that you are going to loose fight retreat and don't waste fleet. You are just feeding his caps with experience. If u see heavy fortified planet you can always bypass them (kill possible pjs with bombers) or attack from other direction. Usually people attack toward enemy HW, or to disrupt trade and destroy labs (carrier raids with bombers are really good for that). He will rebuild but it cost resources and time.

Get better economy than your enemy and time will work for you.

PS Balance your research (hull, shield, armor, weapons) with what you are building and your fleet size. Sometimes upgraded ships are better than bigger fleet. As You will be watching replays you will see what skilled players do.

I usually fill my fleet points do some ship upgrading, fleet up fill fleet points ....... But there are much better players than me out there. It comes down to microing.