I'm going to refer to it the same way he does:
The Warm Up
Simply put, the Warm Up is an exercise that is mostly non-diatonic (so it doesn't follow a regular scale) and is more about developing good left and right hand technique and less about music theory. In fact, I'm pretty sure we can ignore music theory for a minute on this one.
We will start at the lowest string (E for guitar, G for ukulele*) with our index finger. Number off your fingers from index to pinky as one two three four. This should correspond to the first four frets of the instrument. So, first finger, first fret and so on. Now play the tab below:
Notice that we are moving ascending chromatically up each string four notes regardless of any music relation.
The point here is not to make music, although you can do it in a rhythmic way. The point is to develop our left hand fingers' touch and the tone we get on the instrument. Also, we can either pick or finger pick the strings and work on our right hand technique as well.
Now, once we have done this up to this point, we need to move back down the strings again. Before we do this, we slide up one one fret. Then, play your way down in the following fashion:
That was actually a question I got. Like how I did that?
You can do that if you want. But, by following the pattern above, you are breaking your fingers up from thinking going-down-a-string-is-always-descending.
Now, once you have gotten to the highest point you are comfortable playing (something like twelve or fifteen frets; maybe ten if you are on a soprano ukulele) we need to come back down the neck. We'll do this in a similar fashion, only this time we will descend on each string. So, it will look like this:
The Good Part
So, this is a good exercise and I encourage you to do it slowly and thoughtfully at first trying to get your fingers doing things right rather than fast. Once you can work your way up and down without any mistakes, you then want to get out our good friend Mr. Metronome.
The examples I have for you above are in eighth notes. Playing at a slow speed, say 60 bpm to start, work through the exercise up and down without stopping. Once you can do this in time at whatever speed you started at, move up a few clicks (like say 63 in our example) and try it there.
The goal with developing speed is starting slow. You need time working something slowly to get the muscles in your hands working together and using their memory (muscle memory) first before you can speed up.
Bonus
Four bonus for today:
1) After going up and down, take a moment to stretch out the muscles in your fingers and hands. Think like you are a soccer player. You would end up with a major injury if you walked out of your locker room and started playing a game without a warmup and stretch.
2) Do this every day to build it up. You don't always have to start slow. You will know where to start as you get more proficient, but always start at a slower speed than you are wanting to work up to.
3) To work on your swing rhythm, try using the metronome as if it is only clicking on beats 2 and 4. So if you are wanting to go 100 bpm, you need to set it at 50 bpm. Then count 1, click, 3, click to get yourself moving. This will be hard and suck at first, but it will payoff loads later.
4) Finally, the patterns of up and down that I gave you above are a starting point. You can, if you feel up to it, work on alternating fingers in inventive ways. For instance, instead of 1, 2, 3, 4 try 1, 3, 2, 4 going up and then 4, 2, 3, 1 going down. Mix it up and make those fingers start to think for themselves!
* Yes, I know that re-entrant tuning that would not be the highest string. Let's imagine that you have a low G tuning for a minute. Also, ignore the possibility that you own a baritone uke.
