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No sanding needed. Just a thorough wash. That's another advantage to plasti-dip; it is removable and you will still have your stock wheels and paint.

You can mask off the tire if you choose to, but the plasti-dip peels pretty easily off the rubber. One tip would be to tackle the hard to get to areas on the very first coat. Around the edge of the wheel, the lug holes, and the inside/rear of the wheel. For nice smooth coverage, allow at least 20 minutes in between coats and apply 5-7 coats per wheel(I did 6) and make the first coat light for good adhesion.

It goes on very similar to spray paint, but is much more forgiving. Light runs will smooth out as it dries and not show in the finished product(my experience, anyway).
Also, make sure you store the plasti-dip at room temperature before using. If it's too cold when you try to spray it, it will come out in bigger globs rather than a fine mist(was 55F in the garage when I did mine, so kept the cans inside).
Clean the nozzle between each coat. You can do this by carefully peeling off the dry plasti-dip, then holding the can upside down and spraying for a couple seconds to clear out the nozzle. If you don't clear the nozzle between each coat, you will also end up with larger globs.