Visit previous locations that the person used to frequent. Former homes and places of employment are often useful places to talk to people and learn the current location of your target.
Call family members, coworkers and friends of your target if you are on good terms with them to ask for information regarding the person's location. Only do this if you are not worried about your target becoming aware that you're looking for him.
Contact the court and Department of Motor Vehicles if you have a current judgment against your target. The court or DMV may have records regarding a change of address that you can use.
Search online through search engines and social networking sites. Your target could appear in the search results and a current location can often be gleaned from the information.
Stake out a location if you believe your target is currently there. Keep your vehicle a decent distance away to avoid being spotted and if you follow your target to another location, maintain at least a two car length distance away. Blend into the environment as best as possible and wear nondescript clothing so you don't stand out.