I'm going to pick up trombone here soon for Jazz band because not too many trombones try out, so I was wondering if any of you had some advice or tips.

Thanks A Lot!!!

Since you already play a couple of brass instruments some things will carry over. But you'll have to get used to a way bigger mouthpiece, using a lot more air, and probably the hardest thing for most converts, the slide. It's easy in the sense that each slide position corresponds to a valve combination, but developing the muscle memory to land in the right spot every time will be a challenge. Most valve players I've heard that switch to trombone tend to be very smeary and sloppy with the slide, and intonation tends to be a problem.
Find a good trombone teacher and get some lessons. That's the best thing you can do for yourself. Good luck!

I agree with the way bigger mouthpiece. THAT THING IS HUGE!!! It's probably 20 times bigger than my french horn mouthpiece! (Okay, maybe not THAT much bigger, but still, it's big) My band director just got a trombone for me out of the closet today, so today's my first day. The slide is as you said, going to be very hard to figure out. But repitition helps.

I got the trombone out and the slide doesn't move so well, what can I use to lubricate it?

If the horn has been sitting in a closet, it probably badly needs a cleaning. After cleaning , if the slide is still sluggish, regardless of lubricant choice, a trip to the shop for an alignment is probably in order. It's well worth it, believe me.
Last year we did some clinics at some middle schools. The first thing I did was check the slides of every student. Then I showed them with my horn how well a slide can move. The had no idea how good it can be.
Last thing... first rule of thumb when it comes to lube... Just use a tiny bit. More isn't better.

I've been using valve oil on the slide, is that okay until I can find something specifically for trombone slide?