For a description of the symbols, see the section on Action Notation for Tab.
 

The first thing to notice is that there are no bent notes in there!  The most basic blues theme doesn't even have to stay in the blues scale.  This lack of bends makes it a great 12 bars for beginners to practice.  You can make it a little bluesier by bending all the 3 draws down 1/2 to the flat 3rd.  Another thing you can do is to replace the 7 blows in bar 6 with the 6 overblow, which is the same note as the 3 draw bend, but over the IV chord it is the flat 7, which is really needed to match up with the 5 draw flat 7 over the I chord, bar 2.

A variant of Blues Theme 101 moves the phrase over the IV chord in bars 5 and 6 down an octave and makes use of two of the hole 3 draw bends.  Here's how that goes:
Blues Theme 101A - bar 5: | 1>. 1> 2>. 2> 3>. 3> 3". 3" | 3'. 3'  3". 3"  3>.3> 2>. 2> |

Of course the 2 draw can be used instead of the 3 blow since they're the same note.
Blues Theme 101B - bar 5: | 1>. 1> 2>. 2> 2. 2  3". 3" | 3'. 3'  3". 3"  2. 2  2>.2> |

Blues Theme 101 – Cross Harp High

You can also play Blues Theme 101 in the high octave, still in cross harp (2nd position).
 

Once you can play the "Blues Theme 101" in 2nd position on both the low end and high end of your harp, you'll be well on your way to playing the blues.  This theme is probably better to practice than scales, certainly for blues, because it will help you learn to play under the chords and get your ear attuned to where the changes are.

Come back to this theme often.  Use it to practice your new techniques.  Play it with feeling.  Improvise around it, using it as a home base to return to if you run out of ideas.  Don't hurry.. incorporate it into your musical memory.  Be able to play it low or high, low and high, backwards and forwards and inside out.

This position is pretty accessible, but does require the 6 overblow (6#).

This is the easiest position from which to play the theme in 1st position, but it breaks down a little over the IV chord in bars 5 and 6 because the highest notes are not available.