#1
Alright, I want to write guitar instrumentals. What are some things I need to know, scales, modes, improvision, stuff like that?
#2
Hm well, to be as abstract as possibl , listen to jam bands A LOT. You'll find patterns and little formulas and will soon be able to write your own. It's a trial and error process, not much concrete things to say.

Start with...
Allman Brothers
Grateful Dead
Derek Trucks Band
Pink Floyd
Cream
Jimi Hendrix
Phish

Those are the"true" jam bands, Jimi not so much, but he still wrote some great live jam pieces. Have at it.
Looking for my India/Django.
#3
Listen to shred and metal and hard rock and progressive music, too.

Steve Vai
Yngwie Malmsteen
Joe Satriani
Iron Maiden (not instrumental, but have lots of long guitar interludes)
Megadeth (same as Maiden)
Metallica (same as Maiden)
Dragonforce (same as Maiden)
Dream Theater (same as Maiden)
Symphony X (same as Maiden)
Rush (same as Maiden)
Queensryche (same as maiden)
#4
I listen to about every band/artist you 2 listed with the exception of a few. What I'm tryin to say is how do I write music like them. Like scale, modes, n such. I know my basics like penatonics, chords, blues, but I'd like to know some more advanced stuff to work on.
#6
Everyone has to find their own way of going about creating music. That I guess is what makes making music hard.
Gear:
Black Ibanez RG170
Line 6 Spider II 112
Genius Mind