Sell, giveaway or toss unnecessary articles. Clean oily cement floor. Strong overhead light fluorescent or bulb. Orderly storage area, tidy workbench. Organize, hang tools on peg boards, and put things on shelves.
Cure damp smell by placing bag of limestone in damp area.
Clean water heater outside, change furnace filter, make inspection access easy. Brighten basement by painting walls. Yes, it's for sale, too. Tidy it up. Light it up.