I'm by no means an expert, but this approach has always worked for me, even for non-sealed cameras:
Cleaning dirt and grime off a camera or lens housing: using a fluffy microfiber cloth, moist but not wet, wiping in short motions (don't rub/scratch the dirt in!) and shaking out dirt/dust if needed. Rinse, repeat. Literally.
Cleaning
dry stuff (like sand, windblown dirt, road dust, so on) off a camera or lens housing: first go at it fiercely with an air blower. If you have a compressor or
one of these things, that should work better, but be careful not to force dirt into potential openings like zoom lenses or around buttons (which might make them less responsive/not work at all). After blowing off as much as possible, see above.
Cleaning dust off lenses: air blower. If it sticks, a clean, smooth microfiber cloth or the brush on a lenspen.
Cleaning stains, spots, light salt spray off lenses: air blower, then a large size
lenspen. Don't apply pressure, work in a spiral from either the centre out or outside in. Repeat as necessary. The lenspen also has a nice soft brush that's great for clearing off light dust without getting your microfiber cloth out.
Cleaning filters (except for variable ND filters, unless you want a funky "trapped water" effect in your photos): rinse under the sink in lukewarm-to-hot water. After rinsing and air-drying, see above.
I've never had to clean a really grotty front lens element, but I would likely go at it very carefully with a moist, fluffy microfiber cloth (fluffy to pick up dirt well; the smooth ones are good for polishing, not so good for picking up dirt, and it might grind the dirt into the lens' coating) before removing any residue with the lenspen.