Have a couple spark plugs that needs adjusting. Whats the best practise for this?
Yes. Very gently tapping to decrease gap is fine. Most spark plug gap measuring tools also work to gently pry the electrode back. The key is to be careful. It does not take much force to make the adjustment and the insulation around the electrode can be damaged if handled improperly.
Note that while it's common to re-gap copper plugs, the platinum (and other more exotic) plugs that I've seen usually say that they're not to be re-gapped. If you choose to re-gap them, the risk is possible breakage (potentially during operation) as some of those other metals are more brittle than copper and don't appreciate being re-gapped.