Picking Techniques
Basically there are 3 techniques of picking that can be used in playing. Alternate, Alternative, and Legato. First I'm going to explain why they work, what they are used for, and which to use in certain circumstances. Now, let's visualize what each ine means with these symbol's: / = down, \=up
Alternate
First, Alternate - Up, down, etc. Always up, down.
Why go alternate?
You can either pick up or down...
So if you went all down...

Or if you went all up...

You could go twice as fast going up and down...

Ok, now we understand how that one works, but you can get even more efficient, what if you are switching strings and it would more efficient if you broke the up, down pattern?
Alternative
That's where Alternative comes to play...
Let's visualize this one, like what a visual interpretation of a sweep arpeggio...

Now we see how this is more efficient than the others...
Legato
Now this technique has less to do with your picking, but has to do with your fret hand. This one you pick as little as possible and hammer, pull, or slide the rest of the way. This is used for a more smoother sound and in some cases you can play faster using this that picking every note.
Ok, now what does this have to do with anything???
Let's stick it to something and see how it sounds...
Ok, here is the tab, just a 12 note ascending run in E Natural Minor from the F note.
E|-------------------------|
B|-------------------------|
G|-------------------2-4-5-|
D|-------------2-4-5-------|
A|-------2-3-5-------------|
E|-2-3-5-------------------|
All down's
All up's
Alternate D-U-D-U-D-U-D-U-D-U-D-U
Alternative D-U-D-D-U-D-D-U-D-D-U-D When going D-D or U-U, just drag your pick and sweep across the strings
For the Legato: Just pick first note of each triad (the notes) and hammer on the rest...
Now let's apply some alternative (sweep) picking to some sweep arpeggio's. How about G - Em - C - Bm, (all 5th string roots)
D D D D D U U U U U D D D D D U U U U U
E|----------7-10p7----------|---------3-7p3---------|
B|--------8--------8--------|-------5-------5-------|
G|------7------------7------|-----4-----------4-----|
D|----9----------------9----|---5---------------5---|
A|-10--------------------10-|-7-------------------7-|
E|--------------------------|-----------------------|
E|-------------12-15p12-------------|-------------10-14p10-------------|
B|----------13----------13----------|----------12----------12----------|
G|-------12----------------12-------|-------11----------------11-------|
D|----14----------------------14----|----12----------------------12----|
A|-15----------------------------15-|-14----------------------------14-|
E|----------------------------------|----------------------------------|
Listen to it - Sweeps