Not nowing your soil conditions, I'll tell you how we do it here in East Texas on red clay. Now you're gonna hear some negatives from those up North who deal with freezing conditions and have different soil to work with, so keep that in mind.
First, level off your pad and remove the top soil. Here, the top soil is only an inch at most. Try real hard not to dig too deep and then fill in again. Fill material doesn't have the compaction that virgin soild does. If you have to build up the pad to get it level, do it in small lifts. Depending on what you have to compact it with, do it in one inch to four inch levels.
Be sure to figure in drainage when doing your dirt work. It's an aweful lot easier to do now then later.
I'd use 2X4's for your forms for a 4 inch pad that will techically be 3 1/2 inches thick. Your driveway, your garage and most everything else is this same thickness. The only time I'd recomend using 2X6's is if your working on heavy equipment. It's just way overkill for your needs in my opinion.
Level and square your forms. Use plenty of stakes to anchor your forms. Use screws to fasten them and be sure they are lower then your forms so your scree baord doesnt' catch on them.
Dig the inside perimeter of your forms the depth and width of a shovel.
Are you putting in water? Will you need drains? Measure and put these in now. Refill the holes with sand if you have it and use a hose to soak the sand to get it to compact and fill in the voilds around your pipes.
Put down a vapor barrier if yo want one. It wont hurt, but nobody uses them in my area.
Lay out your rebar on a 24 inch grid. Be sure to use chairs.
Once your rebar is in place, or almost done, contact the cement company and arrange for a morning dump. You want the cooler weather for your pour. Their regular customers will already have most mornings covered, so you might have to wait a few days.
When the trucks get there, be sure to have a plan on the route they will take. Also be prepaired for them not paying attention to your route and getting stuck someplace you never imagined anybody going.
My last pour my sub had a trailer full of 3/4 inch plywood to put down for the dump trucks to drive on. We had one get stuck spinning his tires on some sand. The plywood saved us.
A good finish with a power float can take hours and hours to get. Watch a crew work. They never stop moving and will have water bottles that they use to keep the surface wet so they can keep working it.
There's a very fine line from too soft to too late!!
With this said, I'd reccomend you didn't do it yourself and hire it done. Pouring concrete is extremely physical work requiring experience, skill and allot of knowledge on working the material and what it's doing. The bigger the pour, the more critical it is to have a crew who know what they are doing.
