Finder's View Options allow you to control the way your icons look on your desktop and in your folders. You can zoom your icons all the way up to a hefty 128x128 (shown here) or shrink them down to a modest 16x16. There are tradeoffs of course. Smaller icons let you see more files at once while large icons better allow you to preview your files, especially pictures. You can easily experiment with changing your icon sizes as follows.
In Finder, select View -> Show View Options (or just press Command-J). The options are slightly different for items on your desktop (left) and folders (right).
Use the Small/Large slider to select the size of your icons. If you do not want to affect the size of every icon on your computer, make sure to select "This window only" rather than "All windows" when adjusting the icon size in folders.
The Text size pop-ups allow you to adjust the font size associated with the icons, so you can balance your labels with your images. Select where you want the labels to appear by choosing either Bottom or Right.