Wow, I'm actually posting on this forum.
I'm a non-technical player. I've never tried tactical combat, used the simulator, replayed combat or other techy things. I don't play solo games against the AI. Yet I manage to win games on PBW. So I bring a slightly different perspective than Askan. I don't know how to separate art from science but here are some thoughts on successful play.
First, I am absolutely sure Askan knows what he is talking about. I played with him before and you don't want him as an enemy. But I think there are some other considerations.
1. Cash flow. Having fleets depends on cash flow. To get it you need to expand fast and make efficient use of what you have. There are known techniques for rapid expansion.
2. Efficiency. Changes to maintenance ability dramatically alter the size fleet you can maintain for a given cash flow. Empire points put into maintenance pay off. Points put into mineral production are also really worthwhile.
3. Diplomacy. Alliances and manipulation of enemies can make a real difference. Get on the same side with Askan
Get your enemies fighting each other. Here is an example from a recent game: I was #1 empire and #2 and #3 were very close in score. I thought #2 and #3 were going to gang up on me. So I traded planets for ships with #3 and used those ships as part of a fleet attacking #2. #2 thought #3 was in alliance with me and preemptively attacked #3. They fought a long battle while I expanded and cemented my position. I won.
4. Trade. Trade stuff. Don't worry too much about helping another empire as long as you help yourself.
5. Tactics. Figure out a plan to conquer the galaxy--the plan will constantly change but have a plan. Fight wars that you can win. Attack with overwhelming strength. Negotiate and stall when you are weak or out of position. Defend your gains. Guard the choke points. All the usual plus watch out for SEIV stuff like cloaking and stellar manipulation (more on this later).
6. Talismans. (dictionary says that is the plural). I recently found religion. It isn't necessary but never missing from maximum range is really nice. Of course, you probably reduce aggressiveness to pay for religion (isn't that fitting?) so you are vulnerable while researching. Be really nice for awhile.
7. Construction. So you've expanded to 100 planets, got bazillions in cash flow, a great maintenance ability and here comes Askan with his fleet. Quick you need a fleet of your own. But your construction ability is terrible and you haven't put space yards on every planet nor built construction bases and gosh darn it you're dead before you can build that super fleet. Balance in all things.
8. Game Specifications. This time you have your 100 planets, your maintenance, your space yards, your construction and are all ready to produce that devastating 1000 ship fleet. And just when you go to launch number 201, you realize there is a 200 ship limit in this game. And your much smaller neighbor with his 200 optimized religio-organic ships wipes you out. Darn. Things like ship and unit limits, is surrender allowed, will there be AI, size and type of galaxy etc. influence tactics.
9. Stellar manipulation. You've got that back door guarded and are moving your fleet to the front when your opponent opens wormholes in your best systems and blows their stars up. Ooops. Worm hole opening and closing can play havoc with plans and tactics. So get the tech first or win the war before your opponent can get it.
I guess what I am saying is that there is a lot of complexity in the game and, at least for a non-techy fellow like me, no set formula for success.