Have your home's heating and air conditioner serviced before you put the home on the market. Buyers generally don't want a home that needs large investments, like the purchase of a furnace, so if your heater and AC are good, it can appeal to more probable buyers.
For example, have the repair records for work done on your home, along with the contact information for the contractors. This will give the buyer a good idea about the kind of care you took to maintain and improve the home.
Try to sell your old house before moving into your new house. It can be extremely difficult to keep up payments on two residences while waiting to obtain a buyer for your previous home.