C.C.
Back up your phone to your computer (using iTunes - plug your phone into your computer using the USB cable, launch iTunes, and it will automatically begin backing up your phone). Make sure you also launch iPhoto so your pictures and videos back up.
Then, delete any videos from your phone. For me, it's always the videos that eat up all the memory. You may also find that some of your apps use a lot of memory. If there are any you don't use, delete them (you can always download them again from the app store if you change your mind in the future).
I didn't even think about the amount of memory on my phone when I bought it, but now that I'm upgrading to the iPhone 6, I ordered the one with the most memory. I never want to deal with this issue again!