Depends on map size and # of opponents. Here are the extremes:
Keep in mind, I usually play Random Huge Multi-Star maps, or the Aerolian Sector, with all opponents on, so these first two may be out of date.
Single-Star, Small, 1v1, Quickstart: Basically, a rush.
Scouts. Always Always Always have at least 5 scouts going in any game. In a small map like point blank, 3 will suffice, but better safe than sorry. Good intel is your best weapon...except yout real weapons, of course...
Drop one military lab and research Armor and Health boosts, a least one of each to give you an edge.
Build starting Cap(Sova, for me. Build fighters-only to counter enemy bombers, and make sure the Missile Platform is the first special ability you get, with Embargo the second.) Pump out light Frigs as fast as possible.
As soon as you have the Fleet Supply maxed out, attack your opponent. Deploy Missile Platforms manually until you can set off Embargo once, then set them to Autocast.
Take out Factories and Constructor ships first, make sure you replace any frigates that go dowm as fast as you can to get them back into the battle. Your opponent won't be able to because they will have no factories or constructors with which to build more. Keep the pressure on. On the chance that you see a colony ship in their midst, it should take precedent as a target as it may slip out and take a nearby asteroid, which is all it really takes to break a rush.
It's possible they may have gotten a second planet by now, but as long as you keep pressure on, they'll do their best to defend the Homeworld with any factories they have at this second site. If you find it, bring in all yous scouts, turn off auto-explore, and set Attack to Automatic by Right Clicking the Icon. They're no match for the enemy ships, but they'll keep reinforcements from arriving. Once the enemy capitol goes down, send your own into the new site and repeat above steps, leave 3 or so of your Cobalts behind to keep constructors down.
Single Star: Medium, 1-5 players, Quickstart: Depends heavily on starting location, so I don't have as much of a step by step here, but:
Build scouts, find a choke point if you have one. It may not be a true choke point, In which case this will be a bit harder. Try to make sure it's no bigger than 3 planets, though, or you may not be able to hold them off. "Lock down" these planets, researching Ice or Volcanic if you need to, build the cheapest fleet you can to accomplish this. I've found that a Sova, Protev(Left one jump behind your fleet until the fighting's done), and a group of Cobalts will pretty much take care of anything except Desert and Terran militia without backup. On those two, just expect to be replacing alomost all of the Cobalts.
Beyond that, use the advice from my first post.
Huge, Multi-Star: (Aerolian Sector) Quickstart:
Deploy 10 scouts right away. Rush research Star travel, Starbases, and 1st tier fleet upgrade. Build an Akkan as your first Capitol ship, fill your fleet with cobalts, and leave the star system right away to claim one of the 3 neutral star systems in the middle. Preferably, you'll have scouted ahead and chosen which one you prefer. I suggest one that is heavy in Ice Planets. Take one of these quickly in case your Homeworld is attacked. Once you lose your last planet, the game is over.
Lock this entire system down by placing 4 starbases at the star as soon as you are able. Keep your fleet here as well, and keep researching. Get Hoshikos and Javelis as quickly as possible, then research 2nd tier fleet upgrade and 2nd Capitol ship. Build a Sova, then fill the rest of your available fleet with 1/3 Hoshikos and 2/3 Javelis, keeping all the cobalts you had. After this, no plan can really be perfect. Make sure you keep those 10 scouts out there, and Try to ally with whoever is relatively weak, but not doomed. That way, you'll have a weaker opponent turning on you at the end.
This is all off the top of my head. If you have specific questions I'd be glad to answer them.