The hardest technique for me is sweep-picking. I can't even sweep three strings just yet, but right now I'm concentrating more on blues-style soloing because there will always be a lot of shredders who are better than me.
Hey duude..
You wanna know something?
I don't know this may sound unorthodox to you but...
For 3 string sweeps, after a lot of observation and some practice, you don't have to actually upstroke upon recovery from the pull off. (I assume that you do those sweeps with pull offs but if ya don't nevermind)
This is an example which I posted on the Dean guitar forum a few days ago.
A typical 3 string sweep will be like so. This is actually half of a D Minor arpeggio that I cut up and that leads to the full on followed by the 5 stringed sweep. It is done so to make sweeping slightly easier before leading up to the harder one.
|---------13h15p13---------13h17p13--------------------------
|------15-----------15---15---------15-----------------------
|---14-----------------14--------------14--------------------
|------------------------------------------15------------------
|--------------------------------------------17----------------
|---------------------------------------------------------------
What you do is that after 15p13, you don't upstroke. Instead, you use your index and middle finger (or whichever fingers you use) to "hammer" 15 and 14. The objective in this is to make the notes audible.
This is something which I have been observing from years of practice and watching various videos on youtube. So if I am wrong please correct me. My sweeping has been inspired mainly from Matt Heafy from Trivium.
Cheers