The key to sucess at PBW is experience. And I don't mean ship experience, although that is important too. I mean your experience at playing other humans.
Play LOTS of games. Join as many games as you think you can handle, and then find one more and join that too.
The more you play against other humans, (even other newbies) and see what they do, the better you will get. Playing solo games against the AI is
almost worthless when it comes to gaining experience for playing other humans in PBW.
The best AI isn't going to be as challanging as the worst PBW player.
Join games that are already in progress and in need of replacments. This way you can pick up in a game and skip all the boring empire building stuff and get right to the combat. Sure you might get pasted quick, but you can always blame it on the former owner, even if it was your fault.
Be flexible. There is no formula for winning on PBW. The tips given in this thread are things people did in the past to win games that worked well. They might not win in the future, especially if your opponent knows them too.
Protect your homeworld.
Know where your enemies are.
Know what your allies are doing.
Geoschmo