Haree's egg sucking academy for Sins
1) Upgrade any planets you occupy as soon as you can. It's the Planet Icon with a wireframe going over it when you click on a planet and then it is the top left option in that sub menu. It's something like Planet Infrastructure, it allows more population (more income and safer planets) and also more importantly stops new planets COSTING you money and starts them EARNING you money. Hint: The Home Planet always starts off with 1 upgrade not being done, I recommend against AI you spend your starting resources to do this.
2) Build a Cap Ship Factory as soon as you can at your homeworld and get one Capital Ship built, the first Cap you build is FREE!
3) 1 or 2 Research stations of either type are worth getting. In the Tech trees the stuff on the left is the cheapest and best value for money. The upgrade for Terran planets is often a good investment if your homeworld starts as one.
4) Still failing? Set up a game with something like 3v3 in 1 star system. You can make the AIs on your team more powerful, watch what they are doing. They may not be the best tacticians in the world but sounds like you could learn from them anyway.
5) Build Resource Collector mines at captured planets. They are from the Logistic Upgrade icon (Looks like a cog if I remember right) and then the 2 icons on the left hand side, top and bottom are for building mines. Do this as soon as you can, more often than not the first thing you build.
6) You can buy Crystal or Metal on the blackmarket if you really need it quickly. Either do this on the Black Market screen or in the top right of your screen are 2 quick buttons.
7) When the pirates are nearly raiding then make sure you don't lose the bidding war!
8) At the start of the game build as many scouts as you have phase lanes coming out of your homeplanet and as they get built right click the Mangifying Glass icon they have as an ability.
9) Gun defences at planets aren't that helpful other than to back up other defences such as hanger bays, repair bays and star bases.
10) In the long term try to catch a planet that will be a choke point, get it well defended, upgrade it's planet infrastructure and also it's planet defences so that it will be able to take bombardment longer. Use of a Star Base at that planet is recommended. All Star Bases have a researchable ability that means you don't lose control of a planet until after the Star Base has been destroyed, this can be invaluable in high threat areas that you don't have your main fleets near.