No one is better than you at judging when you should come in for tuning:
No longer able to execute any good carving turns on an icy slope?
--> Your edges are dull and rounded. Time to have your edges ground!
Too little speed on gentle slopes?
--> Your base is dry and damaged. Time to have the base refurbished!
Your skis or board judder on long sliding sections.
--> Have the base profile stone gound now!
Generally: Don't just sharp your edges, always grind also the base, because your ski will get "humpy" otherwise.
Binding adjustment at least ONCE PER SEASON!