One of the more aggravating issues with filling out a form is submitting correct data types. Zip codes need to be 5 digits. A phone number field needs 9 digits but it can be 10 (if you add the country code), plus some people add spaces, periods or hyphens in the numbers. Email addresses have to have at least 1 @ and 1 . and the list goes on.
Don’t penalize your users
You don’t want to add too many helper notifications upfront because you can unnecessarily complicate a form. You also don’t want to load a form up with error messages when a user doesn’t complete the task correctly.
Users care about their data, giving it up is about trust and starts a bond of loyalty
You should also take special care to remember the user is voluntarily giving you this information. Don’t require them to do extra work in formatting the data the way you want it, or the way your CRM requires it. Instead your web developer should do that work for you, allowing your users to proceed through a form quickly.
If they do mess up, help them along
If your users make a mistake in your web form, don’t present them with a list of errors, and definitely don’t refresh the page. Instead do what Cars.com does and create a helper window. Now the user is presented with a very quick solution, and they are not disrupted or diverted from the end goal. In fact, this process gives the user more of a sense of continuing down the same path, rather than making them take a step back. Progress is key.