Assuming you have everything cut and polished before it arrives, all the cabinet guys do is to bed the top in RTV silicone to the cabinet base. If things are not completely level they use drywall screws to get a flat base but there shouldn't be a very big gap since you are still riding on an RTV seat. There may be other tricks but this is what I see.
The cabinets under must be strong enough to bear the weight ( seems obvious! ) and level and stable so that the sealant beds to the granite continuously. Use shims under, not screws above. Point supports can raise stresses in the slab, which eventually may crack it. Local to me here in France, the cost of a granite top translates to; Cutting pre-polished leaf to length & width. Polishing cut edges = additional $/metre Forming radii on edge[s] option = + $/metre Cutting holes for faucets, hobs, sinks = + $/ metre.
Some points for DIYers. a] Make sure of your sizes before getting a top cut. It isn't cheap, keep a drawing and give the cutter a copy in case of dispute. b] Design of kitchen layout can save a lot of money; you can minimise cutouts and non- square edges by choosing non-penetrating hardware. My good wife objected to paying good money to park stuff like toasters, kettle, letter-rack etc. on, so her granite is in her working area. Parking areas are in contrasting wood [ or melamine is possible]. c] Having paid good money, remember it is a natural material and may stain if not cleaned immediately after use. Avoid abrasives like the plague- they scratch, and particularly beware of those green-pad things- often they are charged with particles of silicon carbide! d] All granites ain't the same! Beware of getting much softer stone like marble. e] Watch the crafty supplier- A beautiful leaf of best Brazilian Turquoise is often parked right by the showroom door to seduce the wife's eye, so she don't want mundane pink or gray!
I was not happy with the screw idea either but my wife assures me that is what they do and she has built about 150 kitchens with granite in her communities. I will admit the "slam it together" culture thrives in Florida. What do these customers expect for a lousy $800,000
We use wood shims with our granite tops. Then we use a "latex" caulk that will dry hard and will support the entire top. The screws sound like a stress fracture waiting to happen, but there must be enough caulking preventing the cracks from occurring if Mrs. F has over 150 installed.
The other item to be careful of is the sink cutout. You have to support the top while delivering and setting it so you don't snap the top at the cutout.
I thought about it and putting in screws accurately levelled and true in properly thought-out positions and depths, with gentle placement, enables you to get a countertop at exactly the planned height and keep control the mastic bead thickness too. The type of silicone or mastic may be critical, one with a high modulus and gap filling properties perhaps? My apologies to Mrs F, obviously a thinking person.
As one who actually uses the kitchen -Granite tops look great but are totally unforgiving with glass and china ware, one tap and the plate / glass is broken. I hate them - designed by people who dont know why they are there, for people who dont use them. Just my 0.02
When all was said and don I installed 16" granite tiles ,looks great 20%the cost of granite slab.I do agree with the breaking of China on the counter though,but as I don,t do the cooking I did what what the wife wanted.