01: PASS (12 HCP, but only 2 clubs, so can't double)
02: 2D
03: 1NT (with 18 HCP, slightly too strong (1NT overcall should be 15-17), but should demote a point or two for the KQ of clubs)
04: X (although you shouldn't count a point for the J of hearts, you actually have *4* cards in all the unbid suits, which is a bonus)
05: 2C
06: PASS (the singleton K of hearts is probably worthless here)
07: 2C
08: PASS
09: PASS
10: 1S (if the 5-card suit was a minor suit, a double might be preferable)
11: PASS
12: PASS (don't forget that a double would be interpreted as take-out)
13: 1S
14: 1S
15: 2D
16: PASS
17: PASS
18: PASS (maybe you could bid 2C, but the suit is kind of week for an overcall)
19: PASS
20: 4D (preemptive; although arguably the hand is too strong for that here, so could also just bid 2D)