Last longer.. get a condom made for that.
Sucking your first time.. theres no way around that. You will suck your first time. Its that way for everyone.. how are you supposed to do something good if you've never done it before?
If you're real worried about being a bad lay, make sure she orgasms and you will be ahead of atleast 50% of your schools non-virgin males. Being worried is a bad way to go in.. chance's are she'll be able to tell that it's your first time, but if she cums then it probably wont matter at all.
Ok.. starters.
If you want her to even come close to orgasm, a good 15 minutes atleast of foreplay is essential. Fingering her and/or eating her out will do the trick. You can tell when shes fully aroused because her g-spot (located about 4 inches up on the front vaginal wall, feels kinda spongy) will grow from about the size of a pea at the start to the size of a quarter. If you're not gonna eat her out, stay away from the **** because it can be tricky to operate.
If you've never eaten a girl out and want to try, disregard any techniques you've seen in porn. A good basic one is pretend you're writing the alphabet with your tongue. Not your whole tongue, just the tip. The **** is very sensitive, and sometimes the lighter you do it, the better. You could also try flicking the tip of your tongue on it if you wanna mix it up here and there.
As to intercourse, just take it slow as it is your first time. Make sure to maintain a steady rhythym and depth unless you're changing your technique. Changing speed and depth when shes close to cumming could set you back a few steps which you don't want. If you feel like you're gonna bust soon, you can pull out and regain control, and start back at it. Also, sometimes keeping eye contact when shes gonna orgasm can make it more intense for her.
When you do bust, make sure to pull out quickly, as most condom slips happen when you've already come and you're going flaccid. Tie a knot off in your condom, and in the garbage it goes.
All in all, just be aware of what you're doing and how she reacts to it. She'll start taking lighter quicker breathes when shes getting close. If you think you got it in you, males can be ready to have sex again in as little as 20 mins. Take your mind off of stessing to get up again, and focus on pleasing her for that time. Foreplay works as a good time filler.. just be careful with her **** because they get super sensitive after an orgasm.
Go in thinking you're a sex machine, and you're gonna rock her world. If it is bad, shes not gonna go around telling people that you're not cool and a bad lay.. so don't worry about that. Just enjoy it, because sex is a pleasureable and enjoyable thing.
Hope that helped put you in the right direction.