Blues progressions are not hard. The twelve bar blues progression in the key of C is four bars of C, two bars of F7, two bars of C, a bar of G7, a bar of F7, and then two bars of C to end it out. It is a very common progression that you find in lots of music. It is basically I, IV, V, except you do the IV and the V with a seventh. You can transpose it to any key. Key of G is a G, a C7, a D7. Key of A it is an A, a D7, and an E7. That's a twelve bar blues progression. Once your are playing the chord you just start lifting fingers and putting them back down to see how they sound. After a while you get a sound you like. Example, with the key of C, I like to bounce back and forth between the C7 and a C. Just play with the chords and find something that sounds good to you. You will feel it if it is good.
Eight bar blues. Stagerlee is probably the most played eight bar blues song. Easy to practice along with if you want to practice that way. Again, it is just a progression. Key of C, two bars of C7, two bars of F7,one bar of C7, one bar of G7, two bars of C7. Eight bar blues is in sevenths. Play it an in any key, it is just three chords, a I7, IV7, V7. Like everyone says, blues has a feel to it. No one can teach you the feel, but those are the two most used progressions. If you can play them, you can play with most anyone.
If you are so inclined, there is the blues scale. In the key of C, starting on your third string up (C) C, D#, second string (E): F, F#, G, first string (A) Bb and C. You can go up and down inside and out. You can take one note and just play it, whatever grabs you, whatever feels good. Transpose it to any key you want. You can combine the scales with the chords when you get the urge.
When you look at it from a music theory standpoint there is nothing complicated in the blues. It is pretty much three chords. There are a few variations, but those progressions will get you through most blues. To get the feel for it is a task. If you find yourself sad, that is a good time to practice. Pour your heart and soul into it. Get someone you really care about really mad at you, then go out and practice playing the blues. Feeling sorry for yourself is a good thing when it comes to Blues. Blues is more about the presentation than anything. You gotta make them feel your pain. You can't just mechanically play the blues. That's my advise.