From the guide linked above:
After sanding take your case and clean it with soap and water. And then do the final cleaning with your tack cloth, or denatured alcohol and rags.
That's probably the most important line in the whole guide. I might differ slightly with that last bit however. (and this may well be semantics) Always
wipe down your project with a tack cloth immediately before spraying.
The two biggest nemesis to painting, from puff can to downdraft paint booth, are dust and fisheye.
Fisheye is when an impurity (usually oil based) is on the surface, preventing good ashesion of the paint. The paint runs away from the spot, even if its all but microscopic... leaving a blemish in the paint. Think the old Dawn dish soap commercials when they drop a drip of soap in the greasy water. A spec of oil from your hand, an atomized droplet of Armor All, anything of that sort can cause fisheye. So be sure to clean your work thoroughly before spraying.
Second, and this you will encounter more often than the fisheye, is DUST
. It's everywhere, and you are going to have it where you work, no matter what steps you take to avoid it. There are ways to "repair" dust in a paint job, but they take a lot more work and time than a lot of DIY types are often willing to invest. The one single thing you can do to help prevent dust in your paint work, more than anything in my experience, is you guessed it -- that tack cloth. Use it, and love it.