I find one of the best strategies is to trade tech for income, and then ramp up your spending whenever possible to out-produce your opponents. This strategy takes time to develop, so don't get frustrated if you don't see yourself making a lot of money at first. I also find that Corvettes are a good way to inflate my military rating, as they are cheap to build and maintain, and you can build a lot of them very quickly (they won't do much in terms of attack or defense, but by keeping your military rating high, other races are less likely to pick on you). Once you have a strong economy and a "real" military (i.e. battelships or better) start finding ways to culturally assimilate neighboring races who are too weak to put up much of a protest. From there, it's up to you to decide if you want a cultural, technological, or military victory. It takes time to really get the hang of it -- but stick with it, because this is an incredible game.