Do you REALLY know what your tongue is doing?
Last week I spoke of how the middle and back of your tongue is to be lowered to achieve good tone. If you've been reading the forum posts on BluesHarmonica.com you've probably noticed a theme... when students are having issues with notes sounding airy, flat, not at all or squealing... my answer to them is that their tongue is located in a place in their mouth that's offending that reed (commonly trying to bend the note). The fix is to make sure the middle and back of their tongue is lowered.
When giving this advise to a student in front of me, they say "Okay, got it." and when trying, it's not fixed. They swear that their tongue is lowered. I have them open their mouth and the back of their tongue is humped up like a ski jump.
So, what to do.
Go in front of a mirror... open your mouth... place the tip if your tongue behind your lower set of teeth (to mimic what your tongue is doing in the tongue blocking process) and start moving the different parts of your tongue up, down, sideways, etc. to get a feel and visual confirmation of what the tongue is doing. You may be surprised at how challenging it can be to control your tongue.
With practice this skill can be mastered, and your harmonica playing will benefit greatly from it.