I used to do this for concerts. You need to really be showing that you are there for a good time and read the crowd around you. If you can show you are there for the music, then other music lovers will let you in their groups easier. From there you can try and catch an eye from a girl and move from there.
Bars are different.. there’s plenty advice for bars already. I can get girls there all the time as long as you keep your vibe up. You wanna get there early and talk to any regulars/bartenders there. Being in a bar trying to pick up girls mean you need to pick your location perfectly. Don’t be in a area with so much foot traffic where people are bumping into you. Try and get to know the DJ if it’s that kind of bar. If you can do that part, then it’s all on your game from there.