Estimate dates of events when possible, and include your reason for the estimation. When researching a family in Michigan in the 1860 census, looking at the ages of the children told me that the couple was probably married after 1850--meaning they were probably not in their own household at that point in time.
Is it evidence that they were not married in 1850? No, but it gives me some guidance when researching.
It's not proof either, but that's another tip (grin!).