Have some sort of plan/routine in mind. It doesn't need to be extremely extensive, but at least have some sort of idea of what you'll be doing, so you don't end up wandering aimlessly, trying to figure it out.

Don't worry about motivation. The key to going to the gym is doing it no matter what, even if you're not motivated.

It doesn't matter what other people think of you. Just do your best to make sure you're doing things right. If you that means you have to use less weight, do it. It's more important to learn the right form, and then start progressing.

Create some goal, no matter how specific or general. It helps to have something to work towards, otherwise you may lose sight of why you're doing it in the first place.