Check UserForms Controls For Entries

I have created a userform that contains textboxes, option boxes, and comboboxes. I need to make sure that there are no unanswered fileds when the submit button is hit. Preferably Excel would check for empty fields in the userform when submit is pressed. If Excel finds that some fields are empty it would prompt the user to correct the problem before the userform would post the data to worksheet. My efforts so far have prompted the user to change the data, but still posts the data before the change is made. Basically the submit button keeps running through the code right after it prompts the user for the change.

If textbox1.value = Empty Then
msgbox("Please enter information into textbox1")
End If

With this the msgbox appears, but doesn't stop the submit button from posting the incompleted data.