Are you meaning insertion into databse ? Then, amongst the data which you need to insert, have an unique data which will represent the entire set of data. For example, if your saving user information, user email might be considered as primary key. With this key, you can have other extra keys like phone number, user first name etc etc. Based upon these, you can give a 'check for duplicate' button, which will check the database if already similar data exists. if so, it gives a warning. Otherwise, if gives a 'go' message, after which you can insert the data.
Another addition is, when you 'insert' data, set some $inserted to a value. when you refresh the form set this to another value. Before 'insert' code executes make sure that either the $inserted is 'null' specifying the data is fresh or a value corresponding to reset'ed form. This will ensure that the data is inserted only from a new form or a form which has been reset. This will prevent you from inseting data from the form, in case the form has been accessed by pressing back button in the browser. May be, I am wrong in this idea, but that was just an idea
