It is easier to find families than individuals in the census. Families allow you to verify that you have the right person based on the names of the other family members. For example, it is often hard to search for an individual with a common name such as John Smith if you are not absolutely sure where he was living at the time. Whereas, if the name of John's wife is Matilda and they have children named Lisa and Durwood, you can be fairly certain you have the correct family no matter what location you found them.
One approach is to strart with the most recent census before an individual's death. If the person was married and you know about when both people died, chose the most recent census before when the first person died. That way, you can verify that you have the right person in the census by the combination of the two names. This census will give you at least the approximate year this person was born and place of birth if you did not already have that information. Use that information to search for an earlier census. Sometimes, you can get lucky and you will find one or more grandparents living with the family in their old age. That also will make it easier to search for earlier census records using a grandparent's name.
Some of the online sources of census records allow you to search for multiple census records at the same time. Try to include as much information as you can in those searches. Include spouse's and children's names so that you can narrow your search results. I like to use the census records at Ancestry.com. Since I have my full family tree online at Ancestry.com, it is handy to use their search capability which automatically fills in the search information and the results include the census records among their varied record types.
The information in the census varies a bit by year. For example, the 1900 through 1930 U.S. Federal Censuses asked for an year of immigration to the U.S. This is helpful when searching for ship manifests. You can see the layout of the various census forms over the years at Ancestry.com.
Online sources for census records:
If you are not sure that searching for a census record is the next best option for your research, consider using the advice feature of this site. This will help you pick your next best steps in your research. Go to Genealogy Search Advice.