Playing vs humans

[JenMax]

Another thing to consider. If you are small, and cannot expand, consider quality. Build the very best repair facilities you can - dedicated repair base(s) with three repair pods. (Yards are limited to ONE per ship/base - not repair pods.) Now your small fleet is constantly retrofitted to your best designs. Coupled with interior lines, you much safer against any but an all out massive enemy offense.

[Marty Ward]

The most important thing I've found when playing against humans is to forget everything you did against the AI, they probably did it too and know how to beat it.
I've only played hotseat so maybe some of this is irrelevent.
The game is about economics. Build your economic base and protect it.
Ally with the AI any time you can. Try to get them to fight the other humans.
Try to be the first player, it seems the order of the player determines who fires first in some combats.
If you are a better defensive player than offensive try to get the game started with a high number units and low number of ships allowed, this favors the defense.
Get yourself familiar with all the techs you don't normally play. Learn the strengths and weaknesses of them. The beauty of this game is every thing has a counter but only if you know what everything can do.
Research SM fast. Suicide star destroyer ships can even out a game VERY fast.
Finally, HAVE A BLAST! I'm like you, I've only won a minute fraction of the games I've played against humans but this game has given me the most fun of any game I have ever played in my life.