You can play a solo, but when they ask you to play a rhythm part on a blues progression you can't play anything better than the usual shuffle or, worse, just three power chords? You know too many chord patterns but you have no idea how to use them even on a simple blues progression? Keep reading.
The problem is, of course, that most guitar players are scared by harmony. Sure, they may know some chord patterns (after all many of us start by learning the "cowboy chords"), but they have no idea how they are built, what are the main notes in them, and more importantly how to modify them in order to be creative while playing rhythm. It's actually much easier than it sounds!
You may have seen advanced jazz or blues players being able to improvise using chords. It sounds impressive, but it all boils down to know how to create your own chords patterns. Of course the best way to learn this is not to start with a full-blown improvisation, but "just" by learning how to play some creative rhythm. Let's see how.
The solution is for us to make friends with an interesting musical interval: the tritone. To hear a tritone (that can also called diminished 5th or augmented 4th) try playing the notes C and F# on your guitar. Yes, it's dissonant! But dissonance is not bad, dissonance is "spice." Too much, and you have ruined your music, but if you don't put any then your music is boring.
In blues specifically the tritone is one of the most used intervals to give that zest that is typical of blues music. Despite the bad reputation that the tritone gets from classical music - where it was often called "the interval of the devil" and used only with extreme care - the tritone sounds great in the right context. It's in fact the interval at the core of most chords used in blues. To see how to use it in practice, watch this video:
The first thing you have to do now is of course to pick up your guitar and TRY all this stuff. No amount of reading (or watching videos) will make up for direct experience. You will also see how it's easy to create some interesting and original harmonies by adding notes on the second or the first string as explained in the video.
By the way, I haven't mentioned this in the video, but this is a great introduction to "jazz chords." Rather than learning all these chord shapes by heart you should see how they are built - as we have seen. There are definitely more jazz chords out there than the ones I have shown in the video, but this will get you started. Enjoy!