Back when I was working in Broadcasting, TV news, commerical production, etc. I was told to do the following:
1) use a little hand pump to blow away what you can.
2) Use a lens brush- use only the kind that has a wee bit of radioactive stuff embedded in the handle to put an electrostatic charge on the brush, and attract dust
3) turn the lens upside down and blow across it. "HA! This will put condensation on the lens and this is as pure and unadulterated as you're going to get.
4) Wipe with high-end lens paper-- always from the center outward-- never circular.
Sometimes we'd be using rented lenses cost north of $10K. I was usually working audio, so I was able to stay away from that stuff as much as possible. I knew a guy that got tagged for boogering a lens. He never worked again in the business. It wasn't his fault; they just needed to hang someone.
Having said all that, I'm not above using a cotton t-shirt on a rifle scope if I need to.
The one thing I can tell you for sure is that your worst fear is getting something abrasive on the lens and then rubbing it. I use a lot of sodium bicarb on my clothes to reduce odor. Baking soda is rather abrasive, so I'm careful to get that off first before tackling anything else. For the most part, I live with it until after season. I use lens caps to keep exposure to a minimum.
Body sweat is another bad one. If you have sweat dry on a lens, you need to dissolve it before doing anything else. The best thing to use is water as pure as you can get it.
I mentioned the breath trick, but distilled water is also good. A steaming tea kettle is a good source. Heck, you can use spit in a pinch, but the problem is that any adulteration to the water will dry into a film. You'll just have to deal with it later.
Cotton swab? On a $10K rented lens, I'd be fired. On a rifle scope, it's up to you. The key is not grinding grit into the lens.
Fingerprints? If you've got a fingerprint or other greasy smudge on the lens, that's where I'd dig out a light Iso-Propyl solution, or maybe a light Dawn solution. Finger prints are really nasty critters and they used to eat coatings, but I think they've improved the resilience of coatings in 40 years. The important thing is to get it off quick and remove it evenly. The big bugaboo was getting fingerprints on the lights. The lens would get hot and the light would heat the fingerprint more than the surrounding glass and you could get an explosion. I saw that happen once on a Sixties-vintage TV set.
