We did some adjustments to landscaping, front and back, repainted interior rooms, removed excess furniture and cleaned the carpeting. Had a new furnace installed and air conditioning added. Hadn't had it for the 30 years we lived in the house, but had it installed to help with resale. (A window air conditioner worked well for us for years, but people prefer central air.) Keeping the house in showcase condition was the hardest part...
Good luck with your sale!