First post here

What solution do you use to clean the surface of your scope lenses? I bought a second hand Ruger M77 Mkii varmint and the Nikko stirling platinum 4-12x40 scope has tough dust/dirt from sitting around without a cover maybe?
Any way, I don't want to wipe it without a solution of some sort, in fear of scratching the lenses.
Suggestions?
TIA