Think first impressions - what will a potential buyer see as negative - starting from the road and entering the house. Replace inexpensive items that are not in perfect condition (mailbox, door hardware, dead or dying bushes, exterior fixtures, etc.), repair, restore, refinish, and spruce up the approach to the house. Give your house a power wash. Everybody sees your mailbox, your driveway, your front door, the front of your house and your front yard. Remove clutter inside and out. Park in the garage if you have one. A manicured and green front lawn may need some planning ahead. If you can't keep up with the various treatments, hire a professional or get a company that specializes in lawn care to do them. Spend a few weekends pulling weeds and controlling bugs. And keep pulling weeds as they show up.
We tend to overlook things we are used to seeing. Get a friend whose taste you admire to help you see things that should be addressed.
Find a good professional photographer to take the pictures to use in online ads.
Look at the front door; add color there.
New shutters, or add shutters. (Just the inexpensive kind.)
Add flowers around the house. If you're selling, go with annuals. Impatiens is good--inexpensive, lots of color, just keep watering.
And do the landscaping Pat and Steve suggest.
If you've got a driveway, put a layer of sealer on top to freshen it up.
Hope that helps.
How about a nice flower garden with roses and other blooms that go all spring summer and fall? Then, for the open houses, a few vases filled with those same flowers in the home...