Want to be a good gamer? Play lots of games. If it takes you 2 to 3 hours to play a 500 point game you seriously need to learn your army. A quick fluid game is not only more enjoyable but helps build confidence in your abilities. I'm pretty sure that no one enjoys having to sit around scratching their ballz waiting for a complete noob to figure out what they're going to do. Quick and easy, that's how we like'em.
Your army is good and very capable of winning. Say it over and over again. I cannot stress enough how helpful it is in the tourney scene to simply have confidence in yourself. Ever heard of the "Attractor Factor?" Basically it means that your mental thoughts will equal your future. It sounds so cheesy, but if you envision the win, you're that much closer to the win. If you're not confidant you may find yourself getting pushed around by the lgs rules jerks.
Be Humble (good winner and loser):
Bad losers suck to play against. I'm sure I've been a bad loser on some occasions but I really don't lose that much. That being said I want to focus on the ego maniac. Yeah, you're probably going to kick the tar out your opponent. At least be gracious and allow them to have a good time. If you want to keep gaming then you'll need to keep finding people to play against. You won't get very far by being smug. Buy'em a drink, compliment their painting. Make the game more than a notch on your bed post. The easiest way is to be humble in your conquest.
This is a lot like be humble but applies to much much more than simply winning or losing. During a game you need to show respect to the other player by speaking clearly, making eye contact, listening to what they are saying and by paying attention. Don't be condescending if they ask for a rule clarification and don't bitch about how "cheezy" X is or how broken they are yadda yadda. You can trash talk a bit so long as you know your opponent is ok with that. I'm not, so don't ask me. Also, if you are a spectator you have no right or obligation to rules-lawyer. I'm guilty of this so often that it makes me sick, I feel bad about it but that doesn't make rules-lawyering OK. As a spectator don't ever ever ever ever ever pick up another player's figs without express permission. I don't care if it's in the graveyard or their case. Keep your grimy hand off the figs. And lastly, let them play. Don't be a distraction. Sit and watch and judge for yourself how much friendly banter is acceptable.
If you're going to play a game learn the rules and know your faction inside and out. To gain success as a gamer you also need to learn the other factions. I've found through the few real ass-whoopn's I've had that they were always a result of me not knowing what the other units/caster/solo was capable of. My word of advice? Buy the books and study them, or at least the faction decks. You'll thank me when you're faced with a new army and still know everything about them, then proceed to tear them apart! :)