Taken from Variables for Weight Lifting and Exercise © 2003 Anthony Sell - All Rights Reserved
It is extremely useful to record the progress and training conditions of each workout.
The minimum requirements for useful comparison at the end of your program should include what exercises you accomplished during each workout, the order of these, how many sets of each exercise were accomplished, and how many repetitions per set.
It is strongly recommended that you record how each set felt to you, as well as having a target number of repetitions on your record sheet to compare with how many repetitions you actually accomplished.
Depending on how in depth you wish to make your records, you may want to include brief notes about your diet that day and the day before, any soreness or injuries that you may feel when you begin, etc.
Examples of such workout sheets can be found here.