According to the National Notary Association, a notary should never notarize any document that relates to himself in any way. If he is personally named or will receive any sort of benefit from the document, notarizing it could open the notary to a lawsuit or criminal charges.
The National Notary Association also points out that a notary should avoid notarizing any document that could result in a financial loss for himself. Indiana's Secretary of State says that notaries are also prohibited from notarizing documents signed by their children, spouses or other relatives.
These guidelines are similar for each state, although they may be worded differently. For instance, the Idaho Secretary of State simply says that notaries cannot notarize any document that could result in a conflict of interest for the notary.