To achieve this, do what the professionals do, and use the right tools. If you want to make sure your cabinets will be securely attached and perfectly level, you have to have a good support system.
Unless you have a team to stand and hold the cabinets while you attach them, you will have to use a jack or other support. You are probably better off Wit this system than having a bunch of people who will just be telling you what to do.
People have used car jacks for this purpose, and there are also jacks specifically designed for this. But all you really need is a T brace that has a horizontal piece attached to a vertical piece. Wedge the cabinet into this brace so it is pushed in tightly against the wall and ceiling or overhang.
You have to be careful about slipping, especially if the floor are slippery. The cabinets may fall off the brace, so it is a good idea to use a few of them. They are cheap and easy to make. If your base cabinets have already been installed, you can use them as a base and just put a short jack on them to rest the upper cabinet on. In a pinch, you could even use a tall bucket with a phone book on the top of it, as long as it is stable.
You have to have find the studs to attach the cabinets to. Do not install the cabinets directly into drywall or wood panels. Today's homes are constructed with studs a standard 16 inches apart. You can use a "stud finder", available at a hardware store to find one, then follow along every 16 inches to find the next ones. Mark each stud in the center for more stability.
You may want to pre drill screw holes into the studs; you have to use a smaller drill bit than the screws you will use.
Before lifting the cabinets into place, predrill holes in them. You will need these holes for wiring, lighting fixtures, any racks you may want to install, etc. Measure the wall and the cabinet and then lift the cabinet into place. Put it securely on your support, leaving at least 18 inches clearance over the counter top.
Fasten the cabinets onto the studs with three inch support screws, screwing through the trim or corner of the cabinet, not the thin walls of the cabinet. This may not always be possible, depending on where the trim or studs are, but try to use as many as possible. If you need additional support, you can use a 1X2 piece of wood placed screwed under the bottom of the cabinet at a stud position.
The best way is to place the bottom strips and put the cabinets on top; this will make support easier. The only problem with this is that you usually have to make some adjustments, and if you have screwed in the supports, you will not be able to do this.
Now you can install the door handles and other hardware, and voila! you have a new kitchen.
