Everyone wants to make his worksheet better & good looking. Mostly people choose fill colours & make it colourful background & all.. But this is very tedious work. While doing this you think, which colour would be good, this one or that one. You always waste your time to think. I'm going to tell you something different.. :
First use your system pictures for background or download other pics which you like.
Then click on Page Layout menu -> Background -> Select you picture -> Insert
Great you've done..!!
(This feature is only for presentation not for printing. You can't make print this background image.)