Update: This page and the video below show images and steps specific to iOS 6 however the steps are basically the same on iOS 7, IOS8 and iOS 9
You can prevent being tracked on an iPhone via iCloud & Find My iPhone several ways - all by various methods of disabling or removing the Find My iPhone service on your phone.
Method 1: Disable the location services
Disabling the location services on your iPhone will prevent anyone from tracking you using the Find My iPhone service. You can either disable all location services for all apps or just for the Find My iPhone service. To access the location services settings, tap the settings icon, tap "Privacy", then tap "Location Services". You can either disable all location services by tapping the on/off switch at the top or scroll down to Find My iPhone, tap it, and then tap the on/off switch for "Find My iPhone"
Method 2: Disable the Find My iPhone Service
You can completely disable Find My iPhone by tapping Settings, then iCloud, then tap the on/off switch for Find My iPhone. You can also delete the iCloud account from the phone by tapping DELETE at the bottom of the screen but be aware this will remove all iCloud services from your iPhone.
Method 3: Change your iCloud/Find My iPhone/AppleID password
If you prefer to leave Find My iPhone functional to track it should it become lost or stolen, but don't want someone else to track you, just change your iCloud/Find My iPhone password. To change your iCloud/Apple ID password, log in to appleid.apple.com, select Manage your account, click Password and Security, then in the center of the screen, click "Change Password". You will then have to enter your new password in your iPhone iCloud settings - be sure that you DON'T give the new password to your stalker!
Any of the methods above, or all combined will help prevent someone from tracking your location on your iPhone.