Start with Fred's guide.
I've been rebuilding an Allstate for over a year!
You won't get a ped that's been sitting for 20 years running overnite - just reality.
Give it time, learn about it, take it apart and clean, lube, inspect everything.
On Jawas, especially check the grounds and the wiring under the start/stop switch. Get the manual from Moped Riders Association.org (?)
Once you have put in the time and effort, the reward of riding will be even better - and safer!
good luck - swarm and destroy!