Why does it matter what you wear to the gym? Well the truth is what you wear says a lot about you and people will judge you off of that. You need some good bodybuilding gym wear to let everyone know you're serious and so you feel comfortable.
When most people think of bodybuilding gym wear they most likely picture what is displayed on the left. A stringer and very short shorts. This is obviously so they can see every muscle and vein and still technically be "clothed" and comply with the gym rules.
My guess is your probably not ready or confident enough to walk into the gym wearing that. Don't worry neither am I. It takes a while to get that point and even when you do, people will constantly judge you but don't worry you'll be huge then and it won't matter.
If this appeals to you go for it. I know it's more liberating to wear less clothing so there is an upside to it.
You also don't want to be this guy at the gym wearing unnecessary accessories while he's on the elliptical basically doing nothing.
Don't go overboard with the gym wear. No need for a bunch of under armour or the nicest shoes or all the fancy sweat bands.
Just stick to the basics and you'll be doing fine.
I always wear a shirt. Just any shirt works. It has to be comfortable though.
If you're self-conscious about sweating than wear a dark shirt but if you like to show off your hard work than make sure to wear a light colored shirt.
You have to find what works for you. For me it's just shirts I've collected through out the years that I don't wear when I'm casually dressed. Find a nice comfortable material and just find shirts just like it.
There's nothing worse than when you can't focus on your workout because you're always adjusting your clothing because it's just not comfortable.
Tank tops are the epitome of bodybuilding gym wear. There also probably not going to be the first clothing choice you're going to jump to. Once you've gained some confidence and some muscle you can start wearing tank tops. That way when you workout you can see every muscle and vein in your arms which will only give you more motivation to lift harder.
The stringers as pictured above may be a little overboard but simple tank tops can be very comfortable and allow you to show off what you've been working hard for.
I usually only workout in shorts because where I live it hardly gets below 50 degrees even in the early morning. There also more comfortable and let your legs breathe.
I prefer shorts that are a good few inches above my knee. Anything lower than that annoys me and I lose focus from my workout.
If it gets cold where you're at then sweats are always a good thing to have on hand. Also if you have "chicken legs" guys have been known to cover them up with some baggy sweats to mislead those around him.
The down side is your legs can't breathe. When I wear sweats I feel as if my legs are suffocating and it takes away from my workout.
Test it for yourself. Go to the gym wearing clothes that aren't very comfortable or flattering and then go in clothes that are very comfortable and make you look good. Tell me how big the difference is in your workout.
I know for me personally it makes a huge difference good bodybuilding gym wear.