I agree, be gently. I have lenses that have been in my possession for 20 years and have only been cleaned a few times. The usual dust will blow off. Some haze will come off very easy. Stuff that does not come off easy is usually from fungus damage to the coating and won't ever come off. So my recommendation is always that if it does not come off easy, then stop. Otherwise you will be the one making those 'cleaning marks' that show up on used lenses