You can't help but adore that cute photo of your husband and son on their last fishing trip, but does it really need to be in the middle of your desk?
Take everything that's not directly related to your work off your desk. That includes photos, magazines, greeting cards, awards, plants, coffee mugs and souvenirs. You can still have some of these items in your office, just in a more remote place.
Have a favorite photo of your family framed so that you can hang it on the wall over your desk. Then you can still look at it every day without it taking up any extra room. Put your plants on a windowsill or on top of a filing cabinet, or hang them from hooks in the ceiling. Build a shelf for your awards and souvenirs.
Finally, pick one or two very important (and small) personal items to keep on your desk.