[Will]

Well, if you manage to get past turn 40, try this.

Build a bunch (7 or 8 should be good) of small attack/raid fleets. The fleets should be around 7-10 ships strong when you're about equal to the AI in tech. Be sure to train them, make them as fast as possible, and use trial-and-error to find what balance of firepower/protection you are most comfortable with. Also experiment with different setups of formations and weapon layouts through the fleet (eg, if you normally have 2 PDCs per ship for Battle Cruiser and above, for your raiding design, cut it to one and insert a modified Version that has only one normal weapon, and is loaded with PDC enough to compensate for the others; may or may not work for you, but try it). Include a supply ship to extend range, minesweeper to get rid of any mines that may be thrown up, etc.

Once you have these fleets ready, raid your nearest AI rival's territory, in multiple places. The AI (much like a human) has some trouble handling attacks from many places at once. Your goal in these raids is not to capture AI territory, or even to significantly damage anything. You want to go after small fleets and lone ships, once in a while going after a small planet with little to no defenses. The point of this is to decrease happiness in the systems, which will cut back on AI resource production. So, while your fleets are disrupting, you're hopefully holding the AI at bay in your buffer systems, and your own territory is safe, so you can build the *real* attack fleet. After ten turns of the disrupting fleets doing their work, most likely around 15-25 of the original 50-80 ships will be left, and you should have a nice 50 ship fleet ready to do the real conquering against a weakened enemy.

This should work out, but I haven't actually played in a while, so... YMMV.