This is how I worked on keeping my cadence up. I found some songs that have at least 90 beats per minute. I listen to them often and when I want to keep my cadence up I get one of those songs in my head (I don't recommend riding with headphones unless you are indoors.)

I also practiced riding in the biggest gear I could and still maintain a cadence of 90 rpms. If my cadence slowed I downshifted. Soon you'll find it is a habit to have higher cadence and you'll be able to keep your cadence in higher gears and that will make you go faster! Good luck!