1. Click on Profile on the blue bar a the top of the screen:
2. Scroll down to the beginning of your Friends list and click on the pencil to the right of the word Friends:
3. Uncheck the box that says "Show Friend list to everyone":
You can't hide your friends from your friends and applications
Unchecking that box will hide your friends list when a non-Facebook friend views your public profile, but it will not hide your Facebook friends list from your friends when they look at your profile. Also, this information will be available to applications and application developers.
In addition, this procedure does not hide other publicly available information including your name, profile picture, gender, current city, networks you belong to, and pages you're a fan of.
Double-check your privacy settings
Most Facebook users have by now gone through the mandatory privacy settings wizard, but you can revisit your settings at any time by hovering over settings in the tool bar on the top of the screen and selecting privacy settings. If you don't do this, a fair amount of your information might be available to the public including the names of your kids and other family members (with links to their Facebook accounts), your relationship status, and where you work.
To find out how your Facebook profile looks to the public, click on Profile Information in privacy settings and then on Preview My Profile...on the upper right section of that page.