What should I do to prepair for the tryouts? I already lift weights and run. It's high school rugby btw.

You'll gain a lot more if you just PLAY PLAY PLAY, PRACTICE PRACTICE PRACTICE.

I wouldn't lift weights, I would concentrate on doing things that you do on the field. Muscle from lifting weights will tire you out in the long run, you'll be slower, and not actually as strong as you would be if you just gained the extra muscle through practice.

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Good point. But I thought I would need to gain some weight because im only 5'6 125 lbs. No fat whatsoever. Oh well, I live on an island where everyone is short.

Generally, you lift during the offseason and you don't lift during the season. Ideally you'll practice year round.

You really can't beat experience though. Play as much rugby as you can, and then when you make the team worry about lifting.

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What position are you going for? It sounds like either scrum half or a wing (If you're fast) from your size. Like everyone has said so far practise will help you the most. Work on your technique a lot especially with tackling. If you've played football forget everything about it for rugby tackles. Practice your passing with a friend.

Learn the secret of the grubber kick

Real men play inside centre.

One of the things you're going to have to learn to do which many people don't do and they pay for it when starting out in rugby is shielding the ball during tackles.

If you don't and a hit knocks it out your forwards will let you know about it.

Scrums aren't fun.

Make sure you release the ball when you got to ground.(get tackled)
Make sure when you pass you look at the person your passing to BEFORE the ball leaves you hands.
If your mate gets tackled and your one of the closest to him, HELP HIM.
If a guy runs at you, dont wimp out. The harder you go the less it will hurt. + everyone loves a big hit.
Stay DEEP, the deeper you are the less pressure there is. You want to catch that ball when you already jogging, running slowly will get you snapped.

Don't lift weights, do push ups and those sorts of things, weights if for bulking up and you don't want that if your fast.
If you are dead KEEN on bulking up do light weights but high reps. Ideally you want to be strong, fit and nimble.

completely depends if you want to be a forward (heavy, more muscle) or a back (speed).

Do running drills and use tackle bags. Make sure your joints are in good form, especially your ankles.

Most defiantly look before you pass, that can not be emphasized enough. Even if a person is right by you, which may not be the case, not looking almost guarantees it won't be a nice pass.
You don't want to be jogging when you catch the ball you want to burst onto the ball and be at a full sprint.
A proper workout program can help you immensely in becoming strong, fit and nimble.

Really the best advice anyone can give you is to keep doin what your doin, practice, and MAN UP.

Rugby can get vicious.