Think Less Time On Your Feet
The other day I was running in the park and I heard a lady who was coaching to other runners behind me giving this tip. I tried it on the remainder of my 8 mile run and it really helped me pick up the speed.
"Instead of thinking of trying to move your legs faster, try to keep your feet on the ground for as little time as possible."
This tip made me feel like I was flying. I tried to think of my feet as being lighter and wanting to be in the air. The minute they struck the ground they wanted to come right back up again. It really helps me speed things up on the days when my feet feel like they're dragging.