David's Tip of the Day: Cross Training
If you're already putting in plenty of daily practice on the harmonica - OR - You've been playing the harmonica for a long time and it's evident that you need a broader understanding of music in order to work better with other musicians - OR - You want to dig deeper into writing music with all of the instruments involved - THEN - it's time to cross train!
Your goal is to gain understanding of how each instrument works in the ensemble. Pick your second favorite instrument to start with (harmonica being #1 of course!) and start down the path of learning it. Go about learning it like the way you would any instrument, with lesson books and a teacher (budget permitting). Your goal is to reach a level where you could hold your own (with some mistakes of course) at a jam session, playing most of the common grooves at a manageable tempo. The focus is not to reach a high level, but to have a basic understanding of how that instrument works... its common patterns... strengths... weaknesses... the different approaches for the different eras of blues... etc.
Not only will you gain a huge amount of confidence in communicating with other musicians, your understanding of the music and how to write it gets better as each month of study passes.
Above all, enjoy the process... once a musician, always a musician... enjoy your daily time of discovery.