I tip my hairdresser so heavily that I can always get an appointment, even on Christmas eve. Strictly speaking, the rule is - you do not tip if your treatment, etc is done by the owner or the senior manager/stylist of the salon, since they charge extra for their superior expertise anyway.. But you tip everyone else. If you have 2 people treating you - say they provide different services - you tip them both. I assure you they will remember you, either as a bad tipper or as a good one. They will treat you accordingly in future. You may notice the difference. For instance, good tippers are welcomed when they arrive and will not be left to wait for attention.
Try to tip at least ten percent; up to twenty if you want to be treated as one of their best customers.