As a repair tech of 25 years, here's my advice.
Blow off loose particles. Use lens fluid(alcohol in a pinch) and tissues, Qtips for small optics. Final polish with breath and tissue/Qtip. No eyeglass products. Blow off any remaining loose bits.
Never rub a dry surface, at least use your breath.
Microfiber cloths should be used with breath method. They also pick up gunk, so run them through the wash frequently without fabric softener.
Lens pens work well at first, but like the cloths, they retain contaminants over time. If used on a sand/dirt encrusted surface, they effectively turn into a sanding disc. It's a good idea to clean the disc with an unused soft toothbrush periodically and just use for final polish.
It's a good idea to clean frequently rather than waiting 'till it looks ugly. Same thing with sensor cleaning. Fingerprints should be removed immediately. In dusty, sandy, conditions, at the end of the day break down your equipment and give it a good cleaning if possible. The mirrors are first-surface coated, so use a very light touch. A toothbrush also works well for cleaning the exterior of your equipment and pay close attention to all the nooks and crannies. Built up dust and dirt is a moisture magnet. Also vacuum out your bags one in awhile.
No canned air, use a rocket blower. Also avoid using air compressors, unless it's confirmed they are oilless and have a moisture scavenging system at the nozzle.
