Now that you've assembled the frame and attached the joists to it, it's time to place the structure on the deck blocks and adjust, as necessary, to achieve levelness (picture). Make the rounds at each deck block, checking for level as you go with a carpenter's level.
If you find you're up too high somewhere, remove the deck block and dig out a bit of soil. A mini-mattock comes in handy for this task, but you may use any small digging implement. Replace the deck block and check again with your carpenter's level. Repeat until you get it correct.
Conversely, if you're too low somewhere, lift the deck frame and insert a "shim" between it and the deck block, thereby raising the level of the deck frame in that spot. Scrap lumber can function as a shim.
You actually don't want the deck to be completely level in every direction. Build in a 1/4-inch slope in one direction (away from the house), to promote drainage.
Incidentally, months after the floating deck is completed, the ground under it may "settle" in places, meaning your deck won't be level anymore. Not to worry: once again, inserting a shim here or there (as described above) should do the trick. This is one of the virtues of small floating decks: they give the novice the flexibility to go back and make adjustments later, with relative ease.
In Step 6 we turn our attention to what's going on in the middle of the floating deck area....