From what I have read on BYC, and what I do, the easiest and most effective way to use it is with a cheap kitchen flour sifter. I bought a metal one with the squeeze-type handle. Always use a dust mask and wear gloves. Inside the coop, I give a good coating of the powder on the coop pellets and even use a turkey baster to squirt the DE into corners but some folks just use an old soda bottle with holes poked in the cap and squeeze it to get the powder into the hard-to-get spots.
In the run, I just sift away until there's a light dusting on everything at ground level. Then I often toss in some dried oak/maple leaves from the yard and let the girls work the DE into the soil with their scratching.
I still have the tiny ants, but so far no problem with flies or other bugs.
Some people dust weekly. I'm slack about it and only do it every two or three weeks, so I might end up with a problem.
Good luck.