Ensure all exterior maintenance is up to date: scrape & paint any peeling paint, ensure gutters are clean, downspout extensions are connected and running at least 5 feet from the home (whenever possible), ensure there is adequate soil & grading around the perimeter of the home, hose down the or powerwash the siding, clear off or treat any growth on the roof.
Remove clutter and organize. Pack as if you're moving. Have a garage sale and get rid of any extra furnishings; donate any remaining items that won't be going with you. Deep clean the entire home and eliminate any odors. The more 'move-in ready' your home is, the better the expected sales price and the least amount of time on market.
Before doing any upgrades or projects, consult with an experienced Realtor to ensure that you are taking on projects that will likely give you a return on your investment.