Price
If a property has been on the market for several months, chances are the price is too high. Dropping the price significantly should generate fresh interest, and, if the new price is right, a sale.
Tidiness
It is alarming how many people say they have viewed a house that was really untidy with clothes and toys thrown all over the place and dirty dishes in the kitchen. For the period of time that you have the house on the market, make sure it's clean all the time so that sudden viewings don't embarrass you.
Presentation
First impressions count. Make sure the property is in good condition and looks presentable from the outside as well as inside. The garden is the first port of call for potential buyers so make sure they want to come beyond the driveway.
Viewings
Make yourself available for viewings at all times and make sure your agent is just as flexible. Brief the estate agent that you are happy to accommodate all appointments, otherwise you could miss out on opportunities.
Odd jobs
Take the time to fix broken cupboard doors or other items around the house; otherwise, this could be off-putting for potential buyers, who may begin to wonder what else could be at fault with the property.
Smells
It may be a cliche, but people are impressed by smells of coffee brewing or freshly baked bread. It's not going to change a disinterested viewer into an enthusiastic buyer, but it creates a more homely environment.