Using filters, you may create reports that only display records from the current user who is viewing the report. For example, you may create a report on this month's Leads that only displays records created by the current user.
To do this:
Create or edit the report.
Click the Add dropdown menu and select Filter.
In the field picklist, select Created By.
In the operator picklist, select equals.
In the value field, enter {!$User.Id}.
Click Ok.
Click Save at the top of the page.