Five minutes of this before every session. It isn't in a key: it uses every fret in a row, which is why it's called chromatic. Its job is to wake up both hands and train them to work together.
One finger per fret in first position: index on fret 1, middle on 2, ring on 3, pinky on 4. Press just behind the fret wire with the fingertip, and keep each finger down until you need it elsewhere. Going down, plant all four fingers first, then lift them one at a time.
Alternate pick: down, up, down, up, two notes per click. Each note should sound clear, with no buzz and no gap when you jump to the next string.
The most common mistake is squeezing. You need far less pressure than you think: press until the buzz stops, then no harder. If your hand tenses, drop the tempo.
Play the way up, then the way down, at a tempo where every note is clean. Raise it by 5 bpm only after two clean loops.