I continue to be amazed at the range of sounds (from horrendous to sublime) that a diatonic harmonica is capable of; admittedly, much of the sound I produce is closer to the former than the latter, but good tone is so essential to playing. I often attributed it to the harp itself ("Oh, so-and-so must have a better or special harmonica.", but good 'ol Jon Gindick plays Hohner Special 20s right out of the box and he sounds a world apart from me playing my Special 20. Part of the trick is using less breath, actually breathing the notes (pushing breath from the diaphragm instead of sucking or blowing), and using vibrato (that creates the kind of echo-like effect and is done by kind of chopping up your breath).

Try practicing vibrato on your chords at first. E.g., draw on the 1, 2, 3, & 4 holes (I believe this is a G chord) at the same time. Now while using a single long steady draw, say: uh-uh-uh-uh-uhhhhh. You can hear in between the uh's the chord resonating and creating a much deeper, fuller tone.

For a nice article on tone, see here:
[www.jt30.com]

For a YouTube lesson on tone by Gindick himself, see here:
[www.youtube.com]

A nice lesson on vibrato by Ronnie Shelllist:
[www.youtube.com]

The really important part to tone is how the harmonica is held/cupped and how one holds their jaw and throat muscles which form the resonating cavity that creates tone. This is why someone that is professional can make a cheap harmonica sing. Ever notice how a really good guitar player can make most of the guitars in the shop sound really good? Same thing for harmonica, too much emphasis is placed upon the instrument when most of the tone is up to the skill of the person. Just IMHO : ^ ))