Openings, Part 7 - I'll Take The I (Common Jam-safe Blues Openings)
My personal favorite way to open a song is to play the opening four bars of the I (one) chord by myself, with the band entering on the IV. The band will interpret the tempo of the song from my playing, so there's no need to count anyone in (tempo errors are more likely to happen when you count the band in verbally). You also don't need to tell the band the feel of the song in most cases (shuffle, slow blues, swing, etc.). What you'll play will be rhythmic, and the use of eighth notes (swing or straight) will tell them the groove. One of the easiest, and most effective ways to do this is to play a bass line. The bass line contains all of the information a band needs to know in regards to feel, and obviously you're showing the bass player the line you want them to play.
Here's one of my songs that uses the shuffle rhythm on the opening four bars...
"Lick Train" on Serious Fun CD by David Barrett
http://www.cdbaby.com/cd/dbjg
Here are three great examples of the harp player playing the bass to open...
"Minor Mambo" by Gary Smith on Blues Harp Meltdown, Disc. 1 CD
"El Gado Rumba Azul" by Curtis Salgado on Hit It 'n Quit It CD
"Telephone Blues" by RJ Mischo on East Meets West : Blues Harp Meltdown Vol. 2 CD
If you would like to study bass lines on the harmonica, here is the lesson that teaches it...
Accompaniment Study 7 - Bass Lines
http://www.bluesharmonica.com/lessons/accompaniment_study_7