It depends on which race you are playing as. Vasari should not look for a fight mid-game, the other races should. It also depends on your strategy. You can either expand, focus on your economy or build up your fleet. If you are getting attacked, build counters to their fleet. Don't expand to much or you will lose alot of money. If you take 1 enemy planet, you will boost your economy, military and research capacity and hurt theirs. Start getting carriers. Hope this helps.