research diplomacy techs like crazy b/c they make all the following trading MUCH easier. also, my numbers are for a galaxy size, abundance, difficulty maxed-out game i am currently winning. just trying out stuff.
Tips:
1) Early = expansion & Economy. funds everything. try federalist and max race points on economy/morale. remember to overlap/stack economic starbases so you can build flagships at 1/turn, aka 'instant military'
military is NOT IMPORTANT, unlike civ 4, because you can stack small ships with all weapons. they decimate all.
2) Military resource. whatever it takes to get them. highest upgrade is +59%. think about what 5 or 6 of them does for you.
3) USE TINY SHIPS. NO DEFENSE
small ships cheaper. more ships = more shots fired. more weapons = more damage/shot
#ships & weapons cumulative, but defenses are not.
cost to upgrade each ship, you can build 10 more
EXCEPTION: I keep 1 elite fleet. 10 or so tiny ships each with 200+HP. THOSE I upgrade.
4) Military rating: is an aggregate ratio. if you have a 200 attack 30/30/30def ship, but enemy has 500, 2 attack 0 def ships. their military is "stronger" and you suffer all the diplomacy penalties.
5) endgame military = speed. now try huge ships, LOTS of engines. attacking only costs 1movement. since my fleet has 85 movement, I can go anywhere within 2 turns and destroy 85 fleets/turn.
by this point you should have VAST tech superiority & military resource, now try DEFENSE. an invincible fleet w/ 85mp = fun.
strategies:
1) Trading resources & Stacking unique structures: sending 20 constructors/starbase & defending = annoying. also, limited to ONE hyperion shrinker/logistics.
Solution: research economics/miniaturization/logistics, trade/give them away. ~20 turns later, trade for their upgraded resource starbases. look for planet they built shinker/logistics on, take it over.
1) Surrendering: I've noticed enemy civs surrender when they've lost a lot of fleet and AT war with you. But during peacetime, I've only seen civs surrender when they have only 1-2 planets left.
Solution: immediately after decimating a fleet, offer a peace treaty.
3) Transports: when auto-rallying, ships only leave planets with 1,000 troops, regardless of modules. annoying for large maps.
Solution: use small (1k troop) transports, and use a lot of them. take over planet(s), offer peace treaty in exchange for tech, influence, gold, etc. take the planets back. rinse/repeat. redeclare war about 6-7 times until enemy catches on and refuses to peace. if they're surrendering anyway, might as well leech all their tech/IP/cash. best done within the same turn.
Balance: (for highest difficulty AI)
1) AI does not counter use of small ships or an all-offensive strategy
AI will build varying ship sizes with countering defenses.
Against fleets of all-weapon tiny ships, with "more ships = more shots fired bonus" my fleets are 10-20x more durable, all techs equal.
2) When using rally points, AI does NOT auto-fleet, unless they are in war or your ships are close. mid-game when my ships have 10+ movement, i can run a few fleets up to AI rally points, declare war, and within same turn destroy a few hundred single ships because they are all stacked & not in fleets.
3) AI WAR strategy. AI has no concept of fronts. Will continue to maintain planet and core defenses, and rally points, sending only surplus towards you. makes taking border planets very easy.