This is the best way I can describe it with my manual transmission :
1 - EOC'ng between 25 and 35 MPH, key already in "start" position.
2 - Push clutch down with foot
3 - Put in 5th gear
4a - Let up on clutch quickly, but not all the way, just enough to "tap the flywheel", is how I like to think of it.
4b - Push clutch back in right away to let engine turn over and start revving.
5 - Re-engage 5th gear and be on my merry way.
When I do it right, there is almost no bump in the start. This might be a form of double-clutching, I don't know.
In 5th gear below 25 MPH, the bump in the bump-start gets rougher. At 20 MPH, I think that 4th gear is best for my car.
But like everyone says, your drivetrain will have a different sweet spot. If I were you, I would find an empty road and experiment with "how low can I bump smoothly in 5th gear". Below 20 MPH, I usually use the starter.
I have been coasting and bump starting for years. I still have my original clutch and starter 107000 miles. Geos were made with PBrakes in all models to my knowledge. Always check to see if you have P/S before attempting shutting your engine off! That is one reason I have no interest in Aveos they are standard with P/S.
Autos are funny animals. I was an auto tech for 16 yrs. Some GM veh. can be towed or coasted forever and not hurt them. Others can't for a couple of miles. Geo automatics are not recommended for towing so be careful with your auto. A few seconds won't hurt you but a long mountain coast consisting of miles could affect it's life. Your pump is the heart of your auto. Manuals don't care as they are lubed by splash affect. Some autos are fine because there split line or fluid level is so high they can get residule splash affect. If not you can burn the bushings and carriers up. If you own a CVT built by GM, can't speak on others no coasting AT ALL if you run out of gas STOP!