When using a quality plugin, like those listed in this article, you shouldn’t have to do much in order to keep your form working properly. You might want to send in a test submission every once in a while to make sure the form is working as it should but that’s about it. Of course, it’s always important to run the updates on your plugins, as the code may be updated to plug security holes, add new features, etc. Once a new update is installed, test the form to ensure that nothing broke during the update.