How to make space on my IPhone?

I always have to delete my pictures so I only have about 20 right now, and I own no videos. I don't fit up a full page of apps and i have about 400 songs but I haven't downloaded them all. I have 16G and i don't know why i don't have enough space!

Go to settings>general>usage and see what's taking a lot of space

Could be the music!