First, know that obtaining large plannets (like terran or desert) first takes a long time and pays off slowly.  Your better off grabbing asteroids and smaller plannets first.

Second, learn the counter.  You can find the information here on the forums.  Learn what units counter which, and then try to match your fleet to counter the enemies.

If you want to play multiplayer seriously, you would likely need entrenchment.  Most online play entrenchment nowadays although there are sometimes some vanilla games hosted.  Generally the vanilla games are going to be newer or more casual players and may be a good place to start.  The best way to learn though is to watch replays if you can of good players.  You should learn what counters what units and what units/caps are capable of doing what things.  I am being vague but without you even having the game yet it is hard to tell strategy.  Reading the strategy forum is generally a good idea to pick up tips.  The best way to learn though is trial by fire through playing good people and by watching replays and comparing how well what you do does next to what someone else does.

[_]-Greyfox

Entrenchment is very worth it.  You can finally leave your empire on conquests with starbases garding your flank and empire.  The balance is better (with the new update ) and 90% of online games are entrenchment only games.   Well worth $10.

Well, I just talked to you online, but please let me reiterate.  Play the AI, learn how to control your fleet, what counters what, and how to get a good economy going.  Once you get the basics, come online and enjoy some competition.