Having a sharp razor is of utmost importance to this task. If you are using a dull blade, it will be painful, inefficient, and ineffective. Holding your leather strap taut, run your blade almost lightly up and down the strap lightly. You want the sharp edge to face you when you're sliding away and to face the wall when you're pulling towards you.
Do this lightly about 40 times to make sure you have an extremely sharp blade.
Your grandpa probably used high lather shaving cream. That'll work, but a good low lather soap will do just as well. To soften my soap, I soak it in a small jar of hot water. I also soak my brush to soften it up.
The 2 most important things to remember during the shave are the angle of the blade and the the tautness of your skin. Hold your skin completely taut and maintain a steady 25-30 degree angle and you're on your way to success. I usually have a towel handy to wipe the blade after I rinse it.
If you're like me, you wish you could look like Magnum P.I. but you end up looking more like a 13 year old with peach fuzz so let's shave it off. Just go slow and find some way to maneuver the blade while keeping your skin tight.