Top 10 Guitar Techniques Used in Shredding
Shredding is a fast guitar playing style. Shredding isn't just a single technique. Its a big term. Lots of different techniques are used in shredding. There isn't a (or more than one) fixed/permanent technique to shred. Shredding is different based on different guitarists. But these techniques are used more in shredding.
Every shredder uses alternate picking. Especially with arpeggios. Instead of downpicking alternate picking is more technical and sounds more unique.

A lot of people think shredding is sweep picking. Well, sweep picking isn't shredding. And shredding could be done without sweep picking but sweep picking is very popular in shredding. Especially guitarists like Yngwie Malmsteen, Jeff Loomis or Jason Becker. Jason Becker is the most prominent sweep picker in this case.

Eruption by Van Halen is a prominent example in this case. While techniques like hammers ons, pull offs, alternate picking, whammy bar abuses were used before this song. But his two hand tapping made the prominent licks that a lot of shredders now follow. Buckethead uses tapping a lot.

Shredding needs chords progression. Hammer on and pull offs are used for chord progressions. Especially for building speed.

Same as hammer on. It's like when you getting a chord its hammer on and leaving when it's pull off.
This image defines pull off.
Its associated with hammer on and pull offs. Legatos are quite used in shredding.

Not sure if I had to say Whammy bar Abuse/use, but whammy bar has lots of different techniques which are used in shredding. Ritchie Blackmore was a regular whammy bar user.
Note: by whammy bar I meant whammy bar uses. Not just the vibrato lever.

Not on top because it may be just a part of alternate picking. And it's not common like alternate picking. Eddie Van Halen used tremolo picking in Eruption for few seconds.
Not sure if it's a technique or not. But most people agree it's a technique. Anyway it has been used in riffs and solos.

I know it's a technique of Whammy bar. And I was running out of items here. That's why I had to include it. But dive bomb is one of the most used and prominent techniques of whammy bar.

Thanks for adding this. I was too confused to add this.
The best is Buckethead for the Slap!