Tap your Feet?: Work on your Rhythm... Work with a Metronome - Part 3
I know it sounds overly-simple to state this, but start by tapping your foot to the metronome before you play to the metronome. Tap your left... or your right... or even better, both, one after another.
If you tap your left (1), then right (2), then left (3) and then right (4) you're now effectively dividing the 4/4 timing of blues into its base duple meter.
Look at example 1.2 in Solo Harmonica Study 1... this pattern is at the heart of most chordal playing in blues harmonica. Notice that beats 1 and 3 are inhales and beats 2 and 4 are exhales. So... strong beats (1 and 3) are inhales and weak beats (2 and 4) are exhales. Which means you inhale on your left foot (beats 1 and 3) and exhale on your right foot (beats 2 and 4).
The most challenging aspect of playing a chordal style (like what's presented in Solo Harmonica Studies 2 through 4) is when improvising in this style, to stay in time... not adding or deleting beats as we switch between single-note playing and chording. This left-to-right sway as you alternate feet takes the guesswork out of where to be in your chordal pattern when your single-note lick is done.
So, common options are:
1) Tap one foot
2) Tap both feet, alternating
3) Tap no feet, but sway left to right
4) Tap no feet, but bob up and down
5) 3 & 4 combined
6) Combination of any of the above
Simply stated, the more you move your body, the more accurate your rhythm (it's harder to rush larger body mass than quick, fast-twitch muscles like that found in tapping your foot).
Being able to tap your foot in time and play a NEW lick can be challenging... just remember to work on small chunks of the song you're studying with the metronome while tapping your foot, you train your foot and mouth together as you study a song.