There will not be one right answer. It isn't for straight people. It depends on what the man who is looking to pick someone up likes.

a shirt that says "fuck me" and pants with a zipper all the way around

En mi situacion trato de ser lo mas sexy possible suerte

I know plenty of gay men your age so for starters ignore all the snide comments above from the homophobes. I'm assuming you know the club or bar caters to the gay community. Every gay club or bar I've been in the people are dressed just like anyone else walking down the road. There are always a few guys who wear tight pants to highlight their package, but most are generally casual. Maybe check online to see if they have theme nights, then dress appropriately.

As for what to do. Just sit at the bar and make eye contact with your target audience. Looking others over, especially their crotch, seems to be common. Don't try to apply rocket science, it's not necessary.

That depends on the bar you visit.
If they have themed nights dress to the theme night that you go to. Also only dress if the theme suits your area of desire.
What is more important is how you present yourself, not what you wear. If you sit quietly in a corner and do nothing more than observe, chances are at last call you will have only been an observer. If you see someone you like say something, even if it is only to whisper in their ear "your ass is theirs"
Yes that line has worked for me.

i have gay friends and they dress decent. Just look good and eye catching. If u have good body assets show it like ur body shape niff arms , six pack or if ur body is simple dress to ur body size