The simple wall plate can make such an impact when you look at a room. The wrong wall plates or dirty plates make the room seem less cared for overall, so keeping those plates in great shape goes a long way toward making rooms seem like they're in better shape, too. Switch plate and outlet plate care is very easy, and even the most involved care takes only a couple of minutes.
Don't Make Them Too Tight
When you install a wall plate, you want the plate to be tightly attached to the wall but not too tightly. If you turn the screw in the plate so much that you see the area around the screw start to bend inward, stop turning -- that's tight enough. Not only will a too-tight screw cause cracks in the plate, but the bend in the middle of the plate could make the ends and corners lift up a bit. That allows drafts to come in; it's common for outlet and switch cavities in walls to have little openings that let cold air in or out of the room.
In addition to not tightening the screw in the plate too much, you want to add insulation to help block those drafts. You can buy special foam inserts that you stick onto the openings for outlets and light switches in the wall. These are made especially for use around electrical switches and circuits, so don't buy foam yourself and try to DIY these insulators. A pack costs very little and shouldn't set your budget back at all. Remove the wall plate, remove any cutouts from the insert, fit the insert in the outlet or switch cavity around the plugs or switches (the inserts will be custom-cut already), and place the wall plate back over the insert, tightening the screw in the plate.
Clean Them With an Alcohol Prep Pad
As you use switches and unplug plugs, the plates will start to accumulate dirt and dust. Cleaning these takes only a couple of minutes and requires no more than a dust cloth and an alcohol prep pad -- these are the little square pads you see nurses use before giving you a shot. You can get them in drug stores and big box stores. Turn off the switch, unplug everything from the outlet you're cleaning, and gently dust the tops of the plates before rubbing the pad along the non-outlet/non-switch surface. If you want to be even more careful, you can remove the plate first. Do not press down with the pad as you don't want any moisture running into the outlet or switch area.
You can go with plain wall plates, decorative plates, and everything in between. Get plates that match the color of the wall for an even better look as mismatched plates can often look dingy compared to the rest of the wall.