My shelf of how-to-write-creatively books is pretty small, but since someone asked me today, I made a quick list:
Claims for Poetry, ed. Donald Hall. Some of my favorite essays on poetry are collected here.
The Making of a Poem, eds. Mark Strand and Eavan Boland. Lovely to read this primer on poetic forms, partly because it includes excellent examples of each.
Words Overflown by Stars, ed. David Jauss. Covers poetry, prose, and creative nonfiction in essays by faculty members at Vermont College of Fine Arts.
Madness, Rack, and Honey, by Mary Ruefle. Love this one. Essays on poetry and everything else.
A Poetry Handbook, by Mary Oliver. Comprehensive, compact, and lovely in a witty kind of way.
Attack of the Copula Spiders, by Douglas Glover. Everything necessary about prose explained here.
Naming the World and other exercises for the creative writer, ed. Bret Anthony Johnston. Prompts! Great for fiction writers.
Reading Like a Writer, by Francine Prose. Cheers me up when writing just seems like a pointless exercise in rejection.
Confessions of a Young Novelist, by Umberto Eco. I haven’t read all of this, but it’s entertaining sometimes since I’m not a novelist.
And there’s The Elements of Style by Strunk & White, plus a bunch of solid anthologies of poetry and fiction. Reading and observing good writing very closely is the best how-to.