I'm 8th in Diplowar because I surrendered for personal reasons
Well Dragonlord and I appear to be doing mostly the same things. I must thank you for starting this thread cause now I know what his secret is
Anyway, here's what I tend to do in games...
1) Get increased mineral extraction because you can never have too many minerals in a game
2) Get increased ship construction to crank out ships faster
3) Get advanced storage because more facilities = more resources
4) Never let surplus resources go to waste. Some people build storage facilities. I tend to build/retrofit ships, and then build storage only if I can't spend my surplus.
5) Units are a waste. Fighters are point defense fodder. Satelites are just for cloak detection. Don't bother with mines unless there's AI in the game, or you want an invisible scout between you and the enemy. When a human player attacks, he usually brings a couple of sweepers with him.
6) Trade colonization tech as early on as possible. If you delay, somebody else is gonna get the tech.
7) If there's AI grab their colonization tech then declare war as soon as you're ready. They're only taking up space on planets you could be using. Not to mention your very existence is usually good enough reason for them to declare war. No need to let such scum live
8) (optional) Get organic tech - This tech lets you crank out ships at a cheap cost FAST. Dreadnoughts in 3 turns without emergency build or SY III is possible. Since most people use PPBs, Organic armor gives you quite an edge.
I don't declare war unless one empire is building too many ships or colonizing too many planets. Other people are most likely worried about it as well, so there won't be any shortage of allies.
Stellar manipulation - I haven't been in a game that Lasted long enough for this to be of any use. It's usually Last on my list of research priorities. Monoliths take too long to build, other techs are too expensive to research.