Can you post a picture?

A picture would be terrific, but off the top of my head...things I'd tell anyone.

Paint the front door a rich, deep red depending on your exterior colors.

A pretty winter (or spring!) themed wreath on the front door.

A couple of pots with evergreen shrubs in them...

I might even put electric candles in the windows to add a welcome home glow.

Good luck with your sale!

Here is a photo

Here is a link that might be useful: photo

Looking at the photo, you already have good curb appeal. I actually wouldn't change anything, other than maybe the potted shrubs that Happyintexas mentioned... but honestly, I don't think you need them.

The only other thing I'd say is something it looks like you're probably already on top of: be sure to thoroughly clear snow/ice from the driveway, walkways, porches, and steps. And if you have any spring/summer photos of the outside, I would include them in the listing photos.

For Christmas, I bought two small artificial shrubs to put on either side of the door. I put lights on them for Christmas, but they add such a warm touch to the house that I'm going to leave them until it's warm enough to plant something real. Your house looks really nice as is, but a wreath or greenery near the door couldn't hurt.

I'd leave it 'as is'. Your house already looks nice. I'm not sure that other greenery wouldn't look tired at this point in the year.

Maybe some light in the windows (soft light), and maybe a couple of artifical potted flowers on the front porch for color? Check Hobby Lobby or make up some. Not real big, just a small splash of color.

This will be a lot of trouble, but it can help in the curb appeal -- assuming it snows more.

When you shovel the walks and drive, don't just pile the snow up alongside. Take it to a less visible spot and pile it there.

Prospective buyers will notice that your place looks nicer than your neighbors-- but likely won't be able to put a finger on just why.

I was there last February when we put our house on the market in an icy snowy winter (Massachusetts)and I freted about the icy driveway. I worked at keeping the drive as clear as possible and put a nice oversized dried flower arrangment on our entry porch (I would take it in overnight if snow was forecast). I was that anxious to make everything picture perfect in that terrible real estate market!. I even staged the entryway with its ultra tidy coats, winter boots etc. (We sold in 8 weeks:))
You might put a big potted plant in that lefthand corner of your porch or a wreath just to brighten. Good luck and hang in there!