I often get asked how to practice guitar scales in order to get the most out of them as it's something that's not explicitly taught and is often misunderstood. A lot of players think practicing scales is playing the patterns over and over until it hurts. This is practicing scales but the technique side only; running up and down guitar scales has little to do with actually making music out of them and is more likely to give you tendonitis... ouch.
1. Get Creative
In my opinion the only use for running guitar scale patterns, apart from improving your technique, is to transfer the pattern from the page to your memory. Once this is done I see little point in repeating the same exercise but a lot of players tend to do this expecting to somehow learn how to phrase and create their own licks. If you're using the CAGED patterns or the 3-Note-per-String patterns then most of your time will be consumed by the memorization process, or rather it'll take a long time for the information to become useful in a musical way. I really recommend the 2 Position System so you can get to the creative part quicker and not lose interest in learning scales.
2. Practice Creatively
Once the pattern is in your head get creative with it; your goal here is to see the pattern on the fretboard and come at it in as many different ways as you can so as to avoid the fingering you used to memorize the scale. Try not to depend on E and A string root notes as this will slow you down later on and restrict you musically. You need to be able to come at a scale from any angle and know where you are in relation to the root notes.
Once you're comfortable in one octave venture out into the next but make sure you're not getting lost. If you get lost just come back to base camp. Imagine you've just moved to a new city and you want to know where everything is, you're bound to take a few wrong turns but there's not problem as you can always go back home. The 2 Position System Patterns are an excellent way to negociate the fretboard in this way.
3. Backing Tracks
Backing tracks are fantastic and thanks to youtube et al there are endless quantities of them in practically any style, scale and key. I really recommend using them in the following way:
Choose a guitar scale to practice and find 4 or 5 backing tracks over which you can jam on your chosen scale. Play over the first backing track a few times but as soon as you get comfortable, move on to the next one. The idea here is to practice dealing with anything that's thrown at you which requires that particular scale and the minute you get comfortable you'll start repeating yourself and this will kill your creativity. Trust me, once you get to the fifth backing track you'll be coming up with some amazing stuff and really breaking new ground with your improvisational skills.
4. Become a Riff Master
One of the most overlooked scale drills is coming up with your own riffs. Again, choose a scale and see how many riffs you can make up. Stay in one octave and on the lower strings if you wish, though this is not essential.
5. Avoid Cliché Practice Exercises
When it comes to improvisation and the teaching thereof, I can't help but question certain exercises that seem to have been handed down from one generation of guitarists to the next and so forth in a rather blind fashion. One of those is playing scales in intervals i.e. in 3rds, 4ths, 5ths and so on. It's one of those exercises that all guitar teachers make their students do because their teachers made them do it and so forth. I have nothing against the exercise itself but it's more related to ear training than practicing scales, plus it goes against my philosophy of practicing stuff you would actually play live rather than endless drills. Therefore, for the purposes of practicing creatively I would say avoid these kinds of exercises for now, especially if you find them tedious as if you don't make your practice time fun or challenging, it tends to become very unproductive.
7. See the Pattern, Not the Fingering
As I explain in the eBook, once you've got the pattern down it's important to forget the fingering and start coming at it from as many different angles as you can. See the pattern on the neck then go in and grab 3 or 4 notes making sure you change up your fingering. One of the benefits of the 2 Position System is that you don't spend hours, days or even weeks learning patterns before you can do this.
8. And Finally, Get Take-away
Not of the food variety, though you've probably worked up an appetite. Make sure you come up with something you can take away from your creative practice session; it could be a riff or a lick or even an entire piece of music. The important thing is to have something to show for the hours you put in, and above all to push yourself to create on a regular basis.