Most smears and smudges can be wiped off by using a clean soft cotton lint-free cloth.
If you need some moisture, do not put any liquids on the lens.
Breathe on the lens.
That produces enough moisture to help with wiping away any stubborn smears.
Remember, you are wiping - not scrubbing.
I just purchased a Nikon D5000. Used it for the first time and noticed a smear on the lens. How do I get rid of it? Also, I need advice on the accessories I need ie... flash, tripod, filters and any other things that are rellevant.