The best thing is to lie on the floor with your feet up on a chair (the edge of the chair at the back of your knees, if that makes sense) I think...but I normally lie on the sofa with my feet propped up on lots of cushions so they're higher than my hips. You can try massaging up your leg to the back of your knees as there are lymph glands there which will drain the fluid away. And daft as it sounds, drink lots and lots of fresh water.
I've been sleeping with my feet on a couple of pillows in bed and that seems to help too!