Open the film back with the switch found on the bottom of the camera. Once open you will probably notice a few things: rust, dust, corrosion and gunk. If there is ALOT of rust, you may want to think about just keeping the camera for parts. Rust and film don't get along well.
To get at the nooks and crannies, flip up the rollers by pressing the red tab and pulling them up and out of the way.
Clean the rollers with a soft, lint free cloth. Don't use any water, only alcohol if you must. One side will probably be gunkier than the other.
With the rollers still out of the way, clean all the crud out from underneath. All surfaces should be wiped down, especially where the film travels.
Swing the rollers back into place and look where the film pack sits within the back. There are some foal seals here. If yours are crumbly or non-existent, replace them with a little from the hardware store.
Put everything back together.
Take this time to now clean this side of the lens element with a soft cloth.
Close the back and turn your attention to the front.