Coming up with the best guitar practice routine is a matter of first deciding what your goals are. For most guitarists when they think of a practice routine, the goal is to improve speed and technique. For some, sight reading may also be an area that needs work, as well as improvisation, soloing, rhythm and timing issues.

First, let's look at where you are. If you don't already know how to play the pentatonic scales and diatonic (major and minor) scales, you need to do that first. Once you have them all memorized, let's look at how to work with those, and chromatic exercises as the basis for the best guitar practice routine for you and your needs.

The most essential thing is to warm up properly first, this way you won’t sustain any injuries through practice. I start with a quick massage of the forearm muscles and a couple of stretches to loosen up the arms, wrists and fingers. Next I would play a tune that I know well, just to get my fingers working. It may be chords or a single note melody. The most effective warm-up exercises I do are the chromatic ones. Try this:
Start on the 6th string…. 1st finger 1st fret, 2nd finger 2nd fret, 3rd finger 3rd fret, 4th finger 4th fret. Now move onto the 5th string. Proceed like this up to the 1st string then come back down again. If you do this SLOWLY and make each note sound crystal clear your hand will start to burn!

Now that you're all warmed up, let's start work. You need a metronome. This is an essential tool. It will help you develop consistency in your playing. Decide on an area you want to improve. It may be alternate picking, hammer ons and pull offs, changing chords etc… Now set the metronome to a slow speed, say 80bpm. Once you’re comfortable with this speed increase it by 10bpm. Continue to do this until you cannot go any faster. Now, this is the time where you set yourself a target. Your target should be 10-20bpm faster than what you can play it at,

After this intense practice session (30 mins), take a break! Your hands will likely be tired, and you've been concentrating which tires your body out. Get up for a few minutes and walk around. Shake out your hands and wrists. Get some water, a bite to eat, whatever.

Now it's playtime. Depending on what you're trying to learn right now, this is always open ended. If you're working on your improvisation, then play with some jam tracks and work on licks. If you're learning a song, now's the time to do that. Spend some time at the end of every practice session doing what's really the most fun to you. You should notice that after having practiced all of your scales, exercises, chords etc and taken a few minutes of break, you're playing better than you have before. Now go practice!