Some trans guy tips from your dad

Don’t try that mascara/arm hair shit. I’ve been passing for more than a year with short, blond arm hair. It’s not an important secondary sex characteristic.
Board shorts (without pockets in the front) do wonders to minimize the width of your hips. Always choose board shorts over swim trunks. Choose them over cargo shorts if it’s appropriate.
Speak from your chest, never from your head.
The goal of binding should not be an entirely flat chest; you should bind for your body type.
GC2b makes the best binders out there, and their products are designed specifically for trans men/transmasculine people.
It might seem useless if you’re pre-T, but working out can be a big help for dysphoria.
Eyebrows are really important to passing pre-testosterone. Muss that shit up. Make them look unkempt.
When you ask for a haircut, make sure the edges in the back are squared, not rounded.
If you have peach fuzz, I would advise shaving it. Cis guys shed theirs when they go through puberty. Shaving can also help with facial hair dysphoria.
Don’t ever buy a binder from Amazon. They run in strange sizes (I was an XXL even though I’m a M in GC2b) and take weeks/months to come. It’s also difficult to breathe in them after a few hours.