Director Tad Stones, he of the animated Hellboy, and one hell of a nice boy himself, has a great and relevant post about directing on the page. He says the kinds of things I'm not only always trying to do myself in scripts, but always trying to get everyone who writes for me to do.
I've found that if you're writing a pilot, or other type of first draft that needs to be a "fun breezy read" then heavy directing on the page is going to send you into revisions. However, for most animation scripts, this here's the gospel. Folks aspiring to be seen as someone who knows how to write animation should check out the link below.