Fwiw, I've been getting more comfortable with sight reading by using this site regularly, about ten minutes a day:
Bass Clef Practice | Music Notation Training
in conjunction with a few Googled materials:
- Bass clef staff (lines & spaces)
- Circle of Fifths in bass clef
- Lead sheets and bass clef Real Book
Also bought a Sly & the Family Stone recorded versions book. Will likely pick up other books as my reading improves.
It can be slow at first as learning any language can be, but then notation begins looking like letters, bars look like words, sections look like sentences.
Learning the order of sharps and flats in order was hard for me at first, then became simple when picking up the bass. Using the inlay dots on the neck, go to the D string third fret (F), and do the same in the A and E strings. (That's F, C, G). Do the same in the fifth fret and seventh frets, this time the A and E strings only. (That's D, A, E, B.) There you go. That's the order of sharps. For the order of flats? Same thing, just backwards starting on B.
Some mental exercises have also helped using the Victor Wooten
"theory is simple" methodology. e.g., how many sharps are there in E Major? (If you know the circle of fifths, this might be just memorization. If you don't, then go through the E Major scale, and see which sharps you hit.) F, C, G, D. For the Eb Major scale, all the sharps in the E Major scale are now naturals, and everything else is flat. How many flats is that? Three. The flatted notes were the naturals in the E natural major scale. Three + four = seven. So when you see three flats on sheet music, it's Eb Major, when you see four sharps it's E major (or their relative minors, i.e., sixth degree of their major scales.)
Anyways, this might be too much info, but it's definitely helped me to read faster, identify key signatures, determine chords within the key, look for borrowed chords or substitutions that don't fit the key, and above all, help to improvise. Hope this helps.