Unfortunately, I can't play every day.
However, I am trying to practice at least 5-10 minutes here and there. What are some good theory or scale techniques/practice methods I should have ready to pull out when I don't want to run through a specific song?
One thing I often do in that situation is pick a scale and play it in different positions on the neck. Or vary it further by double-picking or triple-picking each note, or using hammer-ons/pull-offs.
This video has Joe Satriani showing a few exercises that would fit well in the short time frame as well.
Last but not least, if you have a song you're working on and some part of it is giving you trouble, you can isolate that part in a short exercise that you can do even without going through the whole song.
Practice what you are worst at! Why practice something you have down really well and ignore what you need most? 5 mins isn't much but can do wonders for things you suck at (5m is infinitely more than 0m).
Find what you're not good at and practice that. If you don't know your scales then work on those. If you don't know very many chords learn some more. etc... etc... etc...
If you have 5m to work out do you work out the thing you are strongest at? If you do you'll just become more unbalanced. Now if you wanna be unbalanced that's an entirely different story. Just realize that generally the better you are at something the harder it is to get better. i.e., it takes a lot more time. So you won't get much out of practicing your best things (of course if you neglect them too long they might become your worst things)
Here's a book for you: The 10 Minute Guitar Workout, by David Mead.
It contains a set of simple exercises for everyday practice. Each exercise is exactly two minutes long; day after day you increase the speed of the exercise until you switch to a new set.
The book is also packed with all sorts of good advice, I really recommend it.
I think it depends how far along you are with your theory; if your new to the major scale/modes etc I would suggest running through those whenever you have a spare ten mins or so; if your further along perhaps you might try playing intervallic arpeggios or something similar, these can really help tune your ear for chords/build your fretboard knowledge and help you develop new ways of fingering things.
An example of this might be (Amin Triad [A - C - E {Root, Third, Fifth respectively}]):
Note Order
1 - 5 | 3 - 1 | 5 - 3 | 1
A - E | C - A | E - C | A
Here is what this looks like over the first inversion
$6.5 $5.7 $6.8 $4.7 $5.7 $4.10 $4.7
And over three inversions (slide up to the high A to finish)
$6.5 $5.7 $6.8 $4.7 $5.7 $4.10 $4.7 $3.9 $4.10 $2.10 $3.10 $2.13 $2.10 $1.12 $2.13 $1.17
Try this using other chords; for instance use a major triad; the fingering is slightly different, post here if you'd like me to tab out similar things.
EDIT- This excellent online tab maker is what I used to create the tab
EDIT- To use the new JTab plug as detailed here
One thing I often do is make a list of things I cannot currently do. Of course, these are the things I wish I could do.
An example would be:
These are the things I can work on. And the bonus side effect is that I can easily measure my progress.
When I mindlessly practice a scale, I'm still not sure about my guitar skills a few days later. But with this little list, I can easily evaluate my guitar skills after a few days. "A few days back, I couldn't do this, but now I can!"
It keeps me motivated, and also ensures that I learn skills that I can immediately put into context.
So, just remember this little rule. Find out what you can't do right now, and work on it! This works regardless of the amount of time you get each day.
Modal practice is always useful, as it helps to increase adaptability, and also explores some of the broader richness within the scale. Another exercise I do when just getting a couple minutes in is 2-octave runs across the four strings.
Hang on a second. You can't "practice" theory on a guitar, you can't even practice theory. If you want to (ergh)"practice" (READ: learn) theory, put the guitar down and grab pencil and paper.
You CAN practice scales and chords, the sonic qualities of which you can explain with theory, but you aren't "practicing theory".
Fretboard Logic: learn all of it and hit every form of a given quality (pick one for the session, maj, maj7, 9th, etc.) and touch the whole fretboard in your 10 minutes. Also do the corresponding scale forms. This will help with point 2 below.
Chord Progressions: ii-V7-I, I-vi-ii-V7, etc, in all keys in various positions (see point 1) (circle of fourths is a good way to make it sound more interesting) with the metronome for 10 minutes straight. You will be shredding soon. (This is quasi theory, maybe what you meant by "theory" in the first place). If you aren't into this type of thing (why do you care about theory then :), then practice whatever chords you do use, but in rapid succession with a metronome, to smooth transitions.
Use the metronome the whole time. If you are making the best use of limited time, at least be strict with the metronome.
Are you obeying #3 or cheating? You're going to end up wasting your precious 5-10 minutes if you cheat.
Something I regularly practice whenever I have 5-10 minutes is chord progressions of in every possible fretboard position and every possible set of strings on the guitar.
Most chords can be played in five different positions on the guitar in the rough shapes of the C, A, G, E and D open and barred chords.
The string sets I practice are EDG, ADG, DGB, GBE, EADG, ADGB, DGBE, EDGB, AGBE.
The movement of chord progressions I practice are:
I also practice the different qualities of chords:
