You will need to work out the error checking for each important field.
For example to gather the email address email@example.com you will have to check that it has a valid format. Not to forget that once passed it has to be checked for email validity too.
The above example is valid although does not exist but somebody.somethinATsomeaddress.extension is not.
Anything requiring a number only will have to be checked too although this should be staright forward.