Login to your google account at mail.insertyourdomain.com or gmail.com
Click the Gear icon top right and then Settings
Click the "Fliters" tab and then create a new filter:
Enter the email address the form emails come from... (email@example.com or firstname.lastname@example.org)
NOTE: You may need to change this on the form settings on your site or look at some previous form emails. If it changes depending on who is submitting the form then you will need to change the form to use the same email every time, however you can set the reply-to address as the user's email.
Check the boxes "Never sendit it to spam" and "Also apply filter to # matching conversations". (You may mark other options if desired)
This should prevent your emails from going into spam or being deleted as spam!
If you still have trouble let us know and we can try some other spam prevention tools such as check your SPF Record, and possibly add a domain key, or set your site to send via SMTP.