Grab your C harmonica and practice only a 3 notes structure on a 12 bar blues in the key of G. Here are the notes to practice: D-E-F in the I chord, G-A-Bb in the IV chord, and A-B-C in the V chord. BUT... it is played using all holes on your harmonica.  So, D-E-F are on: -1  2  -2" , -4  5  -5  and -8   8  -9.
G-A-Bb are on:  -2( or 3) -3"  -3' , 6  -6   6 ob and 9  -10  10" . A-B-C are on: -3"  -3  4  , -6   -7  7  and -10  10'  10 . 
The 6 ob( overblow ) can be substituted by 7 blow !
This practice will improve your coordination on the harmonica and help you to overcome the fear of using holes 7-8-9-10.
The first 3x 12 bars are the basic exercise. From there I do 2x 12 bars improvising over the practice notes and use some variations. This is all recorded amplified. Next, I play more variations, this time an acoustic recording. 6x12 bars!
The backing track can be found on:
https://www.youtube.com/watch?v=wTq5z2sHM2E

Smooth Shuffle G - C Harp - 3 Note structure Practice

BenBoumanBlues