Things I'd recommend:
-Go with someone for the first couple of weeks. I was dragged into the gym by 2 other friends who'd go every saturday (I hated it for the first weeks because of the pain).
Fast forward a month later, I was going 4 days a week without them because I was actually into it.
-Don't worry about other people's thoughts on you. In Year 8 and 9 I was very skinny but not anorexic, so since Year 10 I was put on a strict program to improve my health. When I first went to the gym, I was very self conscious about what others would think of me, which added to me hating the gym (check above). NOBODY gives a flying damn about you tbh and nobody is going to judge you based on your starting point. I have full respect for those people who have come to the gym who are slightly on the overweight/underweight side as it takes guts to do so and I respect that.
-I'm going to go against OP's words of advice and say Don't go at peak times. I've never gone at Peak times and I'm quite happy as well. Off-peak gives you access to equipment without waiting, there's less "Hardcore" lifters and less people (Helpful if you're slightly anxious).
-Be Humble. As a beginner, you're liable to making mistakes with your form etc and if someone offers you some pointers, PLEASE show how grateful you are. There's been instances where a form correction has saved someone from serious injury and don't you think it would be nice if someone would look out for you? If you have more courage, Ask someone to check your form and correct where necessary.
-This tip is more aimed at the males, but applicable to everyone. Leave your ego at home.
Nobody cares "how much you lift", if you're doing it with a **** form. Work on consistency and form and the weights will go up with time.
-This tip is also more aimed at males, but still applicable to everyone. Don't just do Arm isolation exercises.
There's a very high possibility your body won't be used to heavy weight, so immediately isolating the arms won't do you any good (not in the beginning anyway).
Work on the main compound exercises:
Deadlift
BenchPress
Squatting
I'd recommend you do these for 1-3 months. They are called compound exercises as they target multiple muscle groups at once and will add serious muscle mass to your body, making you stronger as a whole.
-Don't expect huge gains after the first session. Whether you're tryna get that booteh or thicker arms/legs/chest. It's not going to happen overnight. Don't track progress in weeks, but in months.
-Keep Hydrated! Don't wanna pass out.
-Don't spend your entire time on the phone.
-DO NOT BICEP CURL IN THE SQUATTING RACK.
-Have fun! The gym shouldn't be a chore, but something you enjoy doing. Take Earphones to listen to music, make notes on the lifts you've done.