The automatic hints offered by Ancestry and Family Search are a huge help, but keep in mind two important things:
They aren't always accurate, especially Ancestry's hints from other family trees (always confirm info in the records), and they don't always apply to your person.
They do not represent all the available records; no hint doesn't mean no records!
When you first get started working on your genealogy, it's exciting to go back as far as you can and ignore extended family like siblings, cousins, and their marriages. But these associations can be invaluable in your search for records. For example, sometimes older parents and grandparents might have lived with your ancestor's siblings. You might find a female ancestor's maiden name by way of siblings. Always take the time to add info about extended family. You'll be very glad you did!
Ancestry offers the option of public and private trees. The advantage to public trees is that other relatives might find your info and have additional info to offer you through the site's messaging service. Don't worry: information about living people is hidden on both public and private trees.
Don't enter too much info in search forms. You'll either get too many results or none at all. When searching census records, for example, you can start with simply a first and last name, a birth year (see below), and a state. Common names like John Smith might require more narrowing.
Use date ranges, especially on census records. Census records don't often record exact birth years because people were asked how old they were and not what their birth year was (the 1900 census is the exception). Many people estimated or rounded, and some didn't even know their exact age. It's quite common, especially when researching African American genealogy, to find census birth years that are ten years off or more.
Sometimes your searches have to be creative. If you can't find someone on the census, try searching in many different ways. Look for all males both in a ten-year period in a certain county. Look for everyone with a certain last name in an entire state. On some records, you can try searching by a parent's name. If your ancestor's name is Jane Jones and you're getting too many results, try searching for her sibling, Montgomery Jones, instead. This is one of the many ways that knowing siblings and extended family can come in handy.