Practice these riffs until you hear them in your sleep.
Play each one three times slowly, three times moderately, and then three times fast. Repeat until dogs howl, cats scream and spouses threaten to leave.
Good Morning Riff (from Gindick). This riff is your basic what to do while you're thinking about what to do next. Think of it as a rest riff. Start here and end here. The two hole draw is the tonic so this is a good riff for the I chord. It's not very impressive, but you can't scream all the time. This is like the mashed potatoes in a fancy meal - its good, but not the main dish.
You can play the 3 hole blow instead of the 2 hole draw in all of these riffs, but the 2 hole draw is easier to "punch". The 3 hole blow is wimpy sounding. You would play the three hole blow to save wind. When you run out of breath you can breath out through the three hole and breath in through the 2 hole and it will always sound OK.
The Juke Riff. This is a mainstay of the blues. Learn it forward and then play it backwards. Learn to do it as fast as possible and as slow as possible. One of my favorite songs - Hold That Train Conductor (Try the Otis Rush Version) starts out with a slow soulful version of this riff. Every second Buddy Guy song starts out with this riff. It's good for intro's and fills and needs no bends! Make that 6 hole wail by making your hands and mouth say "Waw-Waw".
Boogie Woogie Blues. This is a great practice piece. Learn it at the same time that you are learning the Juke Riff. The breath patterns are different. Playing riffs involves learning the breathing patterns of the riff as much as which holes to play. By varying the breathing patterns you learn how to control your riffs.
These are mostly draw notes. If you are out of breath when you come down to the 2 hole draw, play the 3 hole blow to get rid of some air. If you pass out while playing this you are doing something wrong.
Now the IV chord notes.
The 12 bar blues here changes to the IV chord which in the key of G is a C chord. Most of the holes are blows.
Note on theory. We are playing cross harp. If you have a C harp you're playing in the key of G. The draw notes on a C harp make a G chord so when we are in the Tonic or I chord we should be mostly drawing notes. When the 12 bar blues changes to the IV chord it is a C. Since we are playing on a C harp the blow notes make a C chord. In blues it is safe to play blow notes when in the IV chord.
Back to the I chord. This repeats the I chord boogie riff.
Now the "turn around"
V chord and then the IV chord
Now the I chord to the V.
The exception will be the riffs where the little menu comes up and it allows you to play in first or third position or correct the key. You still will use a "C harp, but they song key will be "C" or "D" accordingly.