Each chord lasts for four beats. On beat one of each measure, you would play the root of the chord. Now there are three beats remaining in each measure and it’s time to solve the puzzle.
The descending fifths progression in four beats is the most straightforward walking bass solution. Play the root of the chord on beat one and then to go down the scale on beats two, three, and four, arriving another step later on beat one of the next measure. So, Amin7 to D7 would be A, G, F#, E (barline), D.
The customary solution for walking an ascending fourth root movement in four beats is to play the root of the chord on beat one and then to go up a whole step and two half steps, no matter whether the chord is major or minor in its basic quality. So, Amin7 to D7 would be A, B, C, C# (barline), D.
These two patterns will get you through about 85% of jazz because of the ubiquity of the descending fifths (ascending fourths) root movements.
Another easy solution for when the chord lasts four beats is to play only the chord tones as an arpeggio. The chord A (add accidentals according to the chord quality) would be ascending A, C, E, A or descending A, E, C, A; and with the seventh would be ascending A, C, E, G or descending A, G, E, C. Then you proceed to the root of the next chord.
If the root of the next chord is not a step away from the note on the fourth beat, there will be some potentially inelegant skipping to the next root. Again, this is acceptable because the bass line not only maintains its metronomic function but it also travels from one root to the next. However, you can create solutions that are more elegant by combining steps and skips.
Here are some possible solutions for the other root movements in four beats (add accidentals according to the chord quality), but you may invent many others:
A to A (repeated note): A, B, C, B (barline), A
A to A (up an octave): A, B, C, E (barline), A
A to A (down an octave): A, E, C, B (barline), A
A up to B: A, E, C, A (barline), B
A down to B: A, E, D, C (barline), B
A up to C: A, B, C, D (barline), C
A down to C: A, E, A, B (barline), C
A up to E: A, B, C, D (barline), E
A down to E: A, E, C, D (barline), E
A up to F: A, C, D, E (barline), F
A down to F: A, G, F, E (barline), F
A up to G: A, C, E, A (barline), G
A down to G: A, B, C, A (barline), G
There are a couple of other artistic considerations when constructing a walking bass line. One is to go in contrary motion to the direction of the melody when possible. For example, in “Autumn Leaves” with a key signature of one sharp, the D7 measure has the melody notes D, E, and F# ascending on beats 2, 3, and 4. If you use the ascending walking bass solution for ascending fourths in four beats, you have the notes D, E, F, and F# on beats 1, 2, 3, and 4. The E in the bass is dissonant with the D in the melody, and same for the F in the bass with the E in the melody. Simply using the descending fifths solution instead of D, C, B, A will completely avoid this problem. Besides, contrary motion has a more balanced effect overall, even if dissonances don’t exist between the bass line and the melody line.
Another is to animate the bass line occasionally with some swing eighth notes. The easiest implementation of this is to repeat any of the bass notes on any beat of the measure, doing this once per measure. Using “Autumn Leaves” as an example, the Amin7 measure in the ascending pattern could be A-A (swing eighths), B, C, C#; or A, B-B, C, C#; or A, B, C-C, C#; or A, B, C, C#-C#.