PLEASE PLEASE PLEASE, don't use the shaking method.
I'm so sick of people suggesting that new keggers shake their kegs. It's a horrible habit and doesn't get you a better beer anyways.
You risk overcarbing your keg, then you'll have to let it warm up, release the pressure, and start all over. Concidering a "set it and forget it method" will only take you 5-7 days to get a drinkable beer...I don't see the point in rushing it. Besides, regardless of the method, you're beer won't hit it's peak (IMHO) until around 3 weeks on gas.
As for your CO2...you should always have it hooked it, even when you're not pouring. If you don't keep constant pressure on the keg, it will go flat. I typically let me kegs get cold, then I adjust my PSI for whatever temp the beer is (usually PSI is between 12-15). I let the keg pressurize for 30 seconds, then I release pressure. I do this 2-3 times and then forget about it for a week. After 5-7 days, you should have a carbonated beer. Carbonated...not balanced.