in school doing great

Just remember one thing, you never know it all. I don't care how long a driver has been driving or what any old timer says. You never know it all, and you will learn some things all through your career. A big truck can bite you pretty hard, pretty fast. Practice, Practice, Practice.... and stay alert. Don't be afraid, but always respect it. Be comfortable, but not over confident. When the weather is rough and you don't feel comfortable, or you get tired, park it. This is one profession where taking breaks is encouraged. Confidence and stamina will come in time.
When you get with your trainer, listen, watch and ask questions. He will be calling the shots during your time with him. Once you are released, you have to be able to make ALL the decisions. Plan your route well. Finding yourself on a back road, and coming up on a sign that says dead end, or bridge weight 5 tons, or bridge height 11.6 isn't pretty. A few extra minutes getting your route together is time well spent. And don't put 100% faith in a GPS. They are helpful, but by no means perfect.
And you will begin to understand that an empty truck in school, is nothing compared to a 75,000 - 80,000 lbs fully loaded rig. If you are lucky, you will only scare yourself a few times. You go to scaring 4 wheelers, and things can get real ugly real quick. I've seen some pretty bad wrecks in my time. You don't want that.

Some shippers and receivers are in locations that barely have room to turn a 53 ft trailer around. So, be ready to deal with limited space and tight situations. If you can't see when you are backing up, get out and look. G.O.A.L. Some old timers out there will tease you and call you a trainee or rookie, but there is nothing wrong with being sure of what you are about to do, and doing it safely.
( And the old timers know that too ). If you can't see and you back into another drivers truck, then you have a problem that you don't want. And remember, most backing accidents happen in truck stops.

I haul bulk Carbon Black. We are required to have a minimum of 40,000 in the trailer. I'm always between 74,000 and 80,000 lbs. It's a different beast than an empty van or flatbed in school. Especially when you get in the mountains, or wet roads, or snow covered roads. Don't overdrive your ability.

You will most likely go OTR with a company that will run you 30 to 40 days, and you will get 4 or 5 days off. It can be great, or it can make you miserable. So bear that in mind. Lots of new drivers want to go home every couple weeks. Lots of companies promise you that, but few will actually do it regularly.

The D.O.T. is out there and the scales are open, so keep your logs together, and you check your permit book for expired permits. You never know when he will step out and pull you for inspection or check your paperwork & logs. They don't let much slide.
( Some companies make keeping your permits updated your responsibility. They will get you the permits you need, but sometimes they expire, and the company isn't keeping up with it real well, and that can cause you down time at the scale house. )
And the regulations are getting tougher all the time. You are responsible for most all fines. If you are heavy, get a CAT scale, get you axles right. If you are overweight, make dispatch decide whether or not to run. If they make the call to run over weight, they pay the fines. If you make the call, and they don't know about your weight, you pay the fines.

Not trying to scare you off, but lots of new drivers think it's just driving, and driving is easy. There is a lot more to it than just driving. If you stay with it for 2 years, without any real major problems, you'll probably do OK and be in it for a long time. If you begin hating it after 6 or 8 months, might be a good idea to look at some other profession. I ran 13 years and got out for a while. Then, I realized that I'm a trucker, and had to get back in. I have days I ask myself why do I do this, but then I really can't see me doing anything else. You either love it or hate it. I don't know that I love it, I just don't like most of the other stuff I worked at....

Hope I helped. Keep us updated and let us know how you are doing. Good Luck and be safe.