you just make a table showing how the activity changes with the substituent groups, and hopefully be able to draw some conclusions from the data.
For example, is a particular substituent better with H, hydrophobic, or hydrophilic groups, EDG or EWG, size of substituent?
These are the more obvious ones to start with. There are many more but ultimately the SAR only serves as a guide to additional work, it is not definitive.