Assuming this slab is within a heated building at about 70 deg. F or so, the usual recommendation is to provide sawcut joints at 36 times the slab thickness, but not greater than 15 feet, in each direction. For a 4" slab, this would mean 12 foot centres each direction. The columns will probably end up determning the sawcut spacing, since there should be a sawcut at each column centreline. So if the columns are at 20 foot centres, the sawcust should be at 10 foot centres.
The sawcuts should be made with an "early entry" saw that permits sawcutting within 2 to 4 hours of the completion of the floor finishing operation. If they wait to the following day to make the sawcuts, then you have lost some of the benefit of them. For a 4" slab, the sawcuts should be 1" deep if made using the early entry saw.
The maximum length between construction joints should also be specified (perhaps 60 feet?).
You can never guarantee that there will be no cracking, but you can minimize cracking by taking a number of steps, including providing the contractor with a layout of the sawcut joints so that there are no "re-entrant corners" that will initiate a crack, and no projections through the slab that will restrain the slab movement; such projections should be isolated from the surrounding slab.
The maximum shrinkage of the concrete mix can be spacified under CSA A23.1 (eg. you can specify 0.04% maximum shrinkage at 28 days when tested as per CSA A23.1 Clause __). However there is extra cost for the concrete.
I generally don't like a 4" slab because you cannot use the 1.5" coarse aggregate in it, since slab thickness must be at least 3 times the nominal coarse aggregate size. A 4.5" or 5" slab allows use of 1.5" coarse aggregate, which allows design of a concrete mix with less shrinkage than a mix with 3/4" aggregate.
The base under the slab should also be considered and carfully specified.
Curing is best done by covering with polyethylene sheet kept in place at least 4 days, preferably 7 days. If this is not possible, a good curing agent can be used (specify one with a high solids cantent) if the concrete is not CSA C-XL classiifcation (I assume it is not in your case).
There are a number of good publications on slab on grade. Unless the slab is not important (eg. if it will be covered by carpet) I suggest that you get someone who knows about slab on grade to write the specification.
Inspection of the work as it is carried out is also a good idea.
If the slab is exposed to deicing chemicals (such as a parking garage exposed to deicing chamicals tracked in, exterior landscape areas, etc.), then there are important additional requirements.
If the building is unheated, then the sawcuts should be closer.
Slab on grade is best placed after the roofof the building is in place.
Slab on grade is one of the most trouble prone of all concrete elements, so be careful.
Hope this helps a bit.