How do i get my 85 el Camino to get better mpg?

Do not know how many miles you have on engine but if over 50,000 original miles on it I think I would look at installing a new timing chain and gear set, distributor and carburetor. Specially if it has lost original get up and go it use to have. Take a compression test to see what kind of condition the chambers are in, if they are below 115 or any of them below that your loosing MPG there also. Good luck