As already said, know the piece of music well so you can use your thoughts on expression rather than on just finding the right notes. Think in musical phrases
and the goal you want to achieve for each phrase, and perhaps the piece over all.
El McMeen usually is a fairly straight forward player volume and tempo wise. He does play cleanly, accurately, does control volume on individual strings (usually
to bring out the melody line over harmony but also sometimes a particular non melody bass line). He does bring out phrases with micro tempo changes on
individual notes (not changing the meter overall).
For example:
https://www.youtube.com/watch?v=pyZS...st=PL2hj-xumEw
At the end of a phrase note a slight play of note time values (overall tempo stays the same) at 0:11 and 0:49. Helps to give a feeling of closer of the particular phrase.
At 1:10 note the volume increase and shorted chord time values to give and extra punch at that point in the tune.
At 2:28 a bit of emphasis on the bass line.
For example of greater use of tempo variation for phrasing you might listen to this piece of mine:
https://www.youtube.com/watch?v=uC2gmf8kP4c
How much you do of what does depends on the style of music and the particular piece.