Harmonica Blessing #1 - No Wrong Notes!
Your C Major Diatonic Harmonica only contains the notes of the C Major Scale. You can play any hole/note and still be staying away from "bad" notes. On top of that, even if you're going for a specific hole/note and miss it, the hole/note to the left and to the right are harmonies of what you meant to play... it still sounds good! This also means that if you can't even play a single hole/note well, or you're just a little off on your aim, you're playing in harmony... two holes/notes played together sound great. You literately can't go wrong! Thanks to Heir Richter for this wonderful design and note layout.
Now, back to reality. This doesn't mean that someone with little experience will play really nice sounding combinations of notes... they need to study and memorize licks from great players... but there are some more general thoughts that can help them out as well.
When you start to play a lick at the beginning of the twelve bar blues progression, start with a draw note and see where it takes you... all draw notes match the I7 Chord (the chord in the opening four bars). Mix blow notes in, but only as stepping stones (on your way to another draw note... don't hold a blow). When on the IV7 Chord do the opposite.