Finder View Options
To define the settings for the way your desktop files actually look, act and feels, you need to tinker with the View Options.
Opening View Options
To open the view options, click anywhere on your desk and then either select Show View Options from the View drop menu, or use the key combination Command + J.
Changing Settings
View options allows you to change a slew of settings from Icon Size to Grid Spacing, Label Font Size and Position. Reducing the sizes and spacing can of course allow you to fit more and more into your desktop, though if you are sffering from a chronic lack of space on your desktop you should consider using Spaces, or have a spring clean.
Tucked away at the bottom of the options windows are a couple of useful settings, Show Item Info and Show Icon Preview, personally I prefer to have these off.
The last option, Arrange By, allows you to define how the desktop reacts to files placed on it. Selecting the option Snap To Grid helps to keep your desktop arranged in an orderly fashion, though equally you can have files ordered by name, date or any other file property you desire from the available list.