Hammer ons/Pull offs
 

Does anyone here struggle with doing very quick hammer ons and pull offs using scales ? I guess it's just lots of practice.

Never been a problem for me.

I gave guitar lessons to a guy once who had problems doing harmonics. I think he just had clumsy fingers.

Yoshi, there's some pretty good book by Guthrie Govan, who's not just a supreme musician, but a flawless teacher as well. He's written great stuff which might help you work out those hammer on/pull off problems of yours. The book is called "Creative Guitar", something like that. Get hold of its second part: there are lots of useful exercises! Helped me lots!
All the best.

Hammer ons and pull off are pretty simple. I guess it's just a test of quick fingers. (Thank you 15 years of PlayStation :D). What I find tricky is tremolo picking (picking really fast). I guess that's just a test of quick and precise wrist movement which I don't have.

they are pretty simple if you are playing with an amp, otherwise you neverknow if you did them correctly

It can be tricky. Doing hammer ons/pull offs quickly is great but I would just slow it down a little bit and make sure they are clean notes and in time to the tempo and slowly raise it up a notch (on a metronome if you have one) Once you start nailing that, speed er up. Practice will definitely help.