I don't know... soloing is really a nebulous concept that involves varying amounts of theory, skill, ear, creativity, and confidence - each in different amounts depending on the person and the situation.
The way I see it is this.... when you do a solo - regardless of what kind of music it is, or what instrument - you are creating a melody. Maybe you are improvising one, or maybe you are carefully crafting one - doesn't matter.
Considering that, you should know your basic pentatonic minor (typical blues scale), and maybe even fiddle with the dorian mode for a bit of flavour (dorian = 1, 2, b3, 4, 5, 6, b7, 1, or C, D, Eb, F, G, A, Bb, C in the key of C) for flavour. Remember... you're creating a melody! These scales will provide you with the blues "flavour" if you will - the b3 and the b7. From there, you need to look at how to express those flavours.... consider the tone you're using (Kirk Hammet could play the blues on his rig and it wouldn't sound half as bluesy as SRV playing the same notes in the same way on his rig...), consider also string bends, vibrato, etc. (listen to BB King for expression and knowing when NOT to play!!)
Try making up a melody using your scales that you like. THEN try playing the same melody, only bending notes instead of re-fretting them!! (ex. instead of playing C, Eb, F on the third string at frets 5, 8, and 10, try playing those same notes at frets 5, 8, and then bending 8 up so it SOUNDS like the same note played at 10!!!) Same melody... different expression. Also consider bending down.... instead of re-fretting C - Bb, try bending the Bb up a full tone BEFORE you play it so that it will come out sounding as a C, and then let the string relax down to the normal pitch of Bb. Same melody, different expression.
Finally... don't be afraid to harmonize your own notes. This can be challenging and requires a good knowledge of the fretboard, but playing a C and an Eb together will generally sound more "bluesy" than a C played by itself.... depending on a lot of variables in the context that you're trying this, of course...
Hope a few of those thoughts help somebody somewhat...
Chris