DIY clothing is a big part of punk fashion. Things such as patch pants and jackets are a big staple in punk clothing.

Here's an example of patch pants. crust pants are also a thing, they are basically patch pants but the difference is you don't wash them. Patches often have symbols relating to their political beliefs (ACAB/1312, anarchy etc.), and bands the wearer likes.

on patches: i commented this on the above paragraph, but patch placement is important!! don't put political patches on the back of your pants/vest/jacket, it can put you in danger as you won't be able to see who gets offended by your statement. people can come up from behind you and attack you

Combat boots, such as doc martens, are really popular. Converse are also shoes often worn by people in the subculture.

Hair is often dyed in bright colors often in mohawks, deathhawks, or cut in "non traditional" styles

Piercings are also a big deal. Gauges, septum piercings, lots of earrings, lip piercings etc.

Leather clothing- leather jackets, spiked collars/bracelets- are important too. this actually comes from (don't quote me on this, but i did hear this from an elder punk) the fact that right around the time the punk scene began, the greaser scene was ending and many greasers were getting rid of their leather jackets and punks were finding them in thrift stores

Many women would wear traditionally male clothing, and shave their heads.
Men also wore traditionally female clothing like skirts and fishnets.
Punk clothing breaks a lot of gender norms, a lot of people dressed to make people question their gender. Dressing androgynously and many other forms of gender expression was welcomed. Gender expression and gender identity was something many people in the subculture experimented with. gender non conformity is popular in the punk scene

Safety pins are often holding together clothing, or there for fashion.
Safety pins on jackets can often mean that the person is a safe person for trans people to come up to for help.

Some people believe punk is all about the music and political beliefs and do not dress like this (mostly Americans), often for practically. This is often called the hardcore scene.