To illustrate some of what jazzoud was talking about: targeting chord tones, and voice-leading from chord to chord. Starting with a root position Bm7b5, here's how each note might lead via E7#9 to Am7:
Originally Posted by simonjandrews
\ - half-step down (strong move)
Bm7b5 E7alt Am7
A (7) \ G# (3) / A (R)
A \ G# \ G (7)
A \\ G (#9) \ F# (6)
F (5) \ E (R) = E (5)
F = F (b9) \ E
F = F / F#
D (3) = D (7) \\ C (3)
D = D // E (5)
D \\ C (b13) = C
D \\ C = B (9)
B (R) \ Bb (b5) \ A
B \ Bb (b5) / B
B / C = C
B / C \ B
/ - half-step up (strong move)
\\ - whole step down (weak)
// - whole step up (weak)
= - shared tone
Every note in the first chord has two optional moves to nearest chord tones or alterations on the E7alt. Those tones themselves then have various leading options on to the tonic, or its consonant extensions.
(F# would not be a common choice on Am7, but would be on a standard minor key tonic, which could have 6, maj7 or 9 extensions - ie an A melodic minor chord.).
Every note of the E altered scale is in play above, and you can see all the half-step leading options.
You can regard this as the purpose of an altered dominant - to maximise the chromatic voice-leading from V7 to I. (You get an additional half-step move to a major tonic, the traditional 4-3 move; eg D>C# in A major.)
IOW, don't think of the scale as a stack of cool tensions on E7 (which it is, of course) but as various ways of getting to good notes on the Am.
Think linear, like jazzoud said (and Bert Ligon and various others). Most jazz changes are too quick to get much sensible mileage out of exploring a whole scale on each chord. You need to assess the significant notes (ie chord tones) and what their functional role is.
Guide tones (3rds and 7ths) will show you the way (3 > 7 > 3, etc, through the sequence), and other extensions and alterations can lead in similar ways.
But "targeting" chord tones also means planning phrases to land on a chosen chord tone on the next chord (or the one after). How you shape the phrase before the target can vary a lot, and may not always need to adhere to chord tones or even a recommended scale - but of course the further you deviate from chord tones, the stronger your phrase needs to be in itself (melodically and rhythmically).
IOW, there is no need to always follow smooth voice-leading (half-step and whole step moves between chords), but that's the way to get an understanding of how the chords work. (It will also improve your comping skills.)