A mattress pad protects your mattress from those little stains, but it also adds comfort to your sleeping platform. Even if you have a pillow top mattress, use a mattress pad as the first layer on top of the mattress itself.
Almost every sheet set today comes with a fitted bottom sheet. Slip the elasticized corners over the corners of your mattress. For the tightest and smoothest fit, do diagonal corners first. Move on to the third sheet corner, then lift up the corner of the mattress, and place the fourth sheet corner as deeply as possible. The mattress will spring flat with a very smooth sheet covering its surface.
Don't use logic when you're adding the top sheet. Put it upside down on your bed. If your sheet fabric has a print or more colorful side, make up your bed with the bright side facing the top of the fitted sheet. Do a hospital corner on each bottom mattress corner and then pull the sheet up toward the head of the bed. When you fold the sheet down over the top of the rest of the bed coverings, the top of the sheet will have the bright side showing.
Put at least one thin blanket on the bed even if you're living in the warmest part of the country. A blanket gives the look of more lift, so your bedspread won't look so flat. Tuck the end of the blanket under the foot of the mattress. If the blanket is very thin, use hospital corners to make a neat foot of the bed. Smooth the blanket up toward the head of the bed on top of the top sheet.