I've tried looking up how to do them, but I keep getting confused. From what I've read you turn your pick perpendicular to the strings, apply pressure then slide up(I've also heard you have to start fast then slow down for the best sound), but I'm really not getting much noise. What strings should I do one on as well?
i like doing it across the low E and A strings at the same time, but i use different speeds, depending on the sound i want
It's called a pickscrape, not a pickslide - pickslide is misleading. You want distortion, plenty of gain, a relatively thick low e string and you scrape, don't slide. It can ruin plectrums, mind you
Scare on the low strings, doing it with distortion will get you even more noise, and theres really no right way to do it, it's whatever sounds right to you.
I have found that fretting the 2nd fret on the low E string gives it a much better sound. Start at about the 18th fret and dig in with medium pressure and then come down as far as you need to go . I only just found out about the 2nd fret trick. It really does change the feel of the scrape. Hope this helps.