well as far as 12 bar blues goes its 3 lines each with 4 bars, totaling 12 bars. it generall follows a note pattern of I, I7, IV, IV7 and V7, an example in E would be 3 bars of E, One bar of E7, 2 bars of A7, two bars of E, One bar of B7, one bar of A7, and two bars of E. The first two lines of it( first 8 bars ) are the general groove and the last line (last four bars) is the turnaround, then it starts again. you basicaaly improvise a walking line over these chords. Now that does you no good unless you can read basic chords so lets see about that. First make sure you know what note each fret on your bass is, example would be your third fret on the E string is a G. Now to play most basically, everytime ayou see G on the chord sheets, hammer out straight G's, same with any other notes. with this approach you dont need to worry about magor or minor or 7th or anything else, but its boring as heck to. A simple way to spice up the lines is to learn your major scales for every note, it's not tough, they all are exactly the same pattern. Now when the chart says G you can run around the scale, but focus on root, third fifth and octave, they are the preeminent notes in a chord, if the chord is minor only play the root fifth and octave, or, preferably, learn the minor scales and swing over them. Finally if the chord says 7th, just make sure you play the seventh flattened. It sounds overwhelmimg, but honestly its not that difficult. keep practicing, and learn your theory
Think not those faithful who praise all thy words and actions; but those who kindly reprove thy faults. Socrates
Only sick music makes money today.
The life which is unexamined is not worth living. Plato, Dialogues, Apology