Day 1: Chest, Biceps
Day 2: Legs and Abs
Day 3: Back
Day 4: ----Rest----
Day 5: Delts and Triceps
Day 6: ----Rest----
Day 7: ----Rest----
Day 8: Repeat Cycle
I frequently mixed it up. During the college semester, I do 3 days on and 4 days off.
The gains you make by training a bodypart 3 times a week are often deceptive as it is just the pump or fluid retention caused by doms that makes the muscle look bigger momentary. The pump fades away quickly leading some people to believe they have to train the bodypart again to "keep it pumped up" hereby shortcutting themselves from real recovery/growth.
For short bursts you can train lacking bodyparts more frequent, but you gotta watch out you don't overload your total workout volume for too long.