Try this:
1) place fingertips on table and tap (0ne at a time) lifting only the tapping finger. Do this in this order - 5-4-3-2-1-2-3-4-5-4...etc. Develop speed.
2) Now, place youf fingertips (one each) on your bass strings as shown (if you have more than 4 strings, use one string each for ring and little finger). Tap out the same exercises on your strings (do not pluck).
3) On a sheet of paper, write (randomly) the numbers 1 thru 5 (about 4 lines of this will do. ie.
4-3-5-1-2-3-2-2-1-5-4-2-3-4-5-2-3-4-2-3
3-4-5-2-1-1-5-5-3-4-5-2-3-4-1-2-3-4-5-3 ..etc.
Now, pick up your bass and tap the strings using the numbers you wrote as a guide (finger to tap with). Repeat, alternating lines as you practice.
When you're comfortable with this, start plucking the strings instead of tapping.
The above exersice works wonders for most my students.