I used to have a mohawk, wear chains, and spiked bracelets, making a mohawk, and alland embodied other punk-rock attributes in my teens.

Because each section starts with a different verb (ex. have, wear..) I'd actually recommend having the last section "all other punk-rock attributes in my teens" as a new sentence. It just makes the sentence a bit easier. You can also use a different word than 'embodied' but I thought it fit here nicely.

I grew up and even if I am still into rock music, I am always open to new experiences.

Therefore, if someone suggests going to a techno party inat the club, of course, I will go!

Once, I was inat the techno club, and I found it interesting or curious to compare how people act in the rock orand techno clubs.

I changed 'or' to 'and' in 'rock or techno clubs' as I assumed you are comparing the people at rock clubs to the people at techno clubs. If you're comparing, for example, 2 people at the same club - which could be a techno or rock club - using or works there.

If rockers are noisy and chaotic, and sometimes they fight, the techno guys do the opposite t. They stand in line or like the checkerboard and shift from one foot to the other, to the right to the left, with or without active hand movements.

Firs onet was a guy in a leather jacket, w. When we came in, he greeted my friend with a fist bump and then he opened thehis palm on which the small bags were lying.

It might be more natural to say "and opened his palm where small bags were lying"

I asked if it was okay to sell the drugs on the dance floor.

I used to wear chains, spiked bracelets, making a mohawk, and all other punk-rock attributes in my teens.

Can also say, I used to make my hair into a mohawk, wear chains....

I grew've grown up, and even ifthough I am still into rock music, I am always open to new experiences.

Once, I was in thea techno club, and I found it interesting or curious to compare how people act in the rock orversus techno clubs.

"in a techno club" or "at a techno club" sounds better.
can also say "in rock and techno clubs"

If rRockers are noisy and chaotic, and sometimes they fight, t. The techno guys do the opposite t. They stand in line or like they're on a checkerboard and shift from one foot to the other... to the right, then to the left, with or without active hand movements.

What you wrote isnt incorrect but there are better ways to say it. You can also say "if rockers get noisy and chaotic, sometimes they fight".

(It is difficult to describe).

I would just say "It's"

I singled out some people from the crowd.

need to keep the same tense (past tense)

FThe first one was a guy in a leather jacket, w. When we came in, he greeted my friend with a fist bump and then he opened the palm on which thup his palm, where small bags were lying.

I asked if it was okay to sell the drugs on the dance floor.

sounds more natural without "the"

I had time to get used to people smoking people on the veranda, but here they were smoking everywhere and cigarette butts were thrown right on the floor.

I used to wear chains, spiked bracelets, making a mohawk, and all other punk-rock attributes in my teens.

Therefore, if someone suggests going to a techno party in theat a club, of course, I will go!

Once, I was in thea techno club, and I found it interesting orand curious to compare how people act in the rock or techno clubs.

If rockers are noisy and chaotic, sometimes they fight, the techno guys do the opposite they stand in line or like thea checkerboard and shift from one foot to the other to the right to the left with or without active hand movements.

First one was a guyguy was in a leather jacket, when we came in, and he greeted my friend with a fist bump and then he opened the palm on which thhis hand, holding some small bags were lying.

I had time to get used to people smoking people on the veranda, but here they were smoking everywhere and cigarette butts were thrown right on the floor.