Make sure you are well hydrated and drink H20 when you play.
I don't like using lip balms because they clog the harp.
Saliva is really the best lubricant that I've found so far.
I sometimes carefully bite the tip of my tongue to create saliva.
I also point the tip of my tongue towards that back of my head. Then I push the underside of my tongue hard against the roof of my mouth and that seem to activate the flow of moisture.
Then I lick my lips. As time goes on you'll develop an early warning signal to lick your lips so you don't suddenly get stuck with dry lips.
Nervousness and certain medications, caffeine, etc... will also dry the mouth...