Here is an incredible technique builder that will get your scales sounding silky smooth by incorporating sweep picking.
The key to this exercise is that you are utilizing a three note per string pattern that allows a "sweep" to help you get to the next string faster.
If you will notice I am using a generic shape where you are at twelfth position and only using fingers one, two and four in the left hand. The first three notes are E, F and G on the E string.
The picking pattern is down-up-down for the first three notes. After the first three notes you have just completed a down-pick on the E string. Your pick is already traveling toward the A String so there is no need to do an up pick at this point. You can just continue your down pick until you reach the A string.
So what you have is a down-up-down on the E string, and then down-up-down on the A string, and then down-up-down on the D string, and so on until you reach the high E string. So as you can see this is a very efficient way to travel across the strings and enables you to go lightning fast. You can apply this pattern to any scale or mode as long as you have three notes per string.
Now for the turn around, you are only going to play two notes on the high E string. In this case the E and F notes. The E note is and down pick and the F note is a up pick. The reason is because this switches the sweep to an up pick so you can sweep back down the strings again.
After up picking the F on the high E string you continue the up pick by sweeping over to the D note on the B string. Now, as you go back down the strings you are reversing the picking pattern so now on each string you are doing a up-down-up picking pattern.
If you will notice When you come to the end of the pattern back on the low E string. You are throwing in that extra chromatic note (In this case the F# note). This sets you up to loop the entire pattern again starting on the down-pick.
You can try a smaller version of this pattern using only 4 strings for example. The key is maintaining the odd number of notes per string for the majority of the pattern, and an even number of notes per string to do the turn around.
I hope this gets your playing lightning fast. Let me know if you have any comments.