LOL at the video. There's no proper way to use a plectrum... do w/e you need to do to make it sound how you want... JB from august burns red holds his pic inbetween his middle finger and thumb on quite an angle and it seems to be workin for him.
I've used lots of plectrums and I'm currently a fan of the dunlop yellow .73 tortex's
Used to use Dunlop 1mm nylon's (black ones) then switched to Jazz III's as I thought I had my reasons but realized I didn't like them, so back to the dunlop 1mm's then recently I figured id give the tortex .73's a chance as one of my friends had one on him (but no guitar o__O) and I put it in my hand and it really felt good... I'm very picky about tone... I notice a huge difference between a Jazz III and a 1mm nylon and out of a random try I really like these .73 tortexs!