Lean it good and hard, on the ground you can't do any damage. After a minute or so enrichen the mixture and check whether you still have misfiring/vibration on the magneto in question. If things don't clear up in a couple of goes you've probably got something a bit more serious possibly a damaged plug, get someone to look at it.
If you do lean on the ground do not forget to enrichen the mixture for take off, unless you are at a high density altitude airport of course. This is to ensure you have sufficient fuel flow to cool the engine whilst it is at full chat.