I dont know if I'm doing it "right", but a variant on the let go of the handlebars has worked well for me. I get on the bike, while coasting put all your weight into your legs so your butt and hands are barely touching the saddle and bars. You will automatically slide back or forward until you are balanced on the pedals. Wherever your butt is, that's where your seat should be - wherever your hands want to go is where your stem should place the bars.