Firstly, colonise, colonise, colonise! Second, build a weapon platform on each planet fairly early, but do NOT fill the planet with them. You need room for fighters and troops etc. You also need to build new weapon platforms as your research improves and dump the old ones.
Later on when you have troops, you can load 5 into a colony ship then people and colonise. That way they have some minor immediate protection and are happier. Try and research in a balanced way, but I prefer to not research some weapons to avoid wasting research points. Pick 3 or 4 types and stick with them. W/P openers comes from 3rd level (?) stellar manipulation and costs a fair bit, so is a long way from getting. Not necessary early on anyway. The planet builder (level 2) is rather handy if there are a lot of asteroids around, it turns them into a planet!
Mines early on can save your bacon, later on become useless when the enemy can sweep 50+ in one go..
Apart from attack ships, you want a couple of defense ships in each fleet, equiped with PD (point defense) to knock out enemy missiles and fighters, and remember to build minesweepers....
