(1) Normal/light duty cleaning: Nikon pre-moistened tissues (link)
(2) Heavy duty cleaning: ROR/microfiber cloth
(3) Small area/spot cleaning and streak removal: clean Lenspen
(4) High weave density, lint-free microfiber cloth: maintaining those very clean is important. Wash cloths frequently, and keep them in a sealed bag.
big makeup brush
nikon pre-moistened wipes
when I bought my 400 do used, the front element was quite dirty. The above cleaned it up perfectly. if the above doesn't work, being a neophyte, I'd get nervous and consider why and think about maybe using a canon clean and inspect coupon.
I've used the zeiss pre moisten lens cleaning wipe both for lenses and binoculars. These are handy and I usually have one or two in my pocket.
I bought some zeiss cloths on sale and just weren't worth it. they did not work nearly as well as the nikon wipes which I love. Odd there is such a difference, but I see many others on FM mention them too.
I use a rocket blower to get off dust, then a LensPen for smudges or any gunk that gets on them. (will use the LensPen brush that's attached if I'm away from home, since I don't bring the rocket blower out and about.) Been using the Lens Pens for about 6-7 years now and I absolutely wouldn't be without one in my bag. They clean the lens perfectly, no scratches and it takes up almost no space in my bag.