I don't think it has to be said but the first impression at the house begins when a buyer pulls up. What are some qualities you want a buyer to think of when they pull up to your home? Write these down. Then physically go outside and look at your home. Do they match? Do any of the Realtors you interviewed see your home in this way? If not, then you have some adjusting to do. You can do this an easy way by asking the realtors for suggestions about the curb appeal and see what comes of it. While you may be off base with what the real first impression is of your home, you may not need to do anything about it.
Have you driven by those houses with so many plants and sooo many things in the yard that it's uncomfortable to look at? Those are the homes we are talking about right now. You will not make your money back if you go too far and most buyers want simple and easy, if the landscaping looks like it will need a lot of maintenance then it will potentially rule your home off their list at first site.
If you have flags or mementos outside make sure they are in good taste and done right. There are rules to how flags are presented. Did you know that? (Here are flag rules) Garden gnomes freak people out and most don't understand the lawn jockeys. You are better off to not have them.
Keep the lawn neat and organized. The lawn should be short but not burnt. I see this all too often here in northeast Wisconsin. A few tips are below:
1. You should only cut 1/3 off the top of the grass. This keeps it growing and green.
2. Make sure you have a sharp blade. While I sharpen twice a season you may only need to do it once.
3. Trim trees up to 6' (please remember this isn't a definitive guide to plants, shrubbery and botanicals. Always consult a resource if you have questions)
4. Two weeks prior to listing go get some good weed killer and hit everything that offends your eyesight (please read all directions on bottle)
If you have a unique property or something special (i.e. Pool) find a way to showcase it. This is where your realtor should shine! They need to have a plan to feature your unique property. Ask them about it and discuss openly. Sometimes this is as simple as getting the right photo of your home or bringing in someone to do 3D imaging such as Matterport.