I tend to collect great openings and descriptions. Maybe I hope I'll pick up good style by osmosis. But certainly reading good stuff helps improve our writing. I still remember a description by Ngaio Marsh of a lawyer's musty office. So good you could smell the place and practically taste the dusty air.
I'm trying not to go back and rewrite my opening (again) until I finish the whole book. Charlotte Cook of Komenar Publishing says that the ending of a book "informs" the beginning--it tells you what pieces need to be in the beginning of the book. So I really do need to finish the piece before I start poking around it again, and again. I am prone to do that, and everyone advises against it--at least everyone I've ever heard talk about writing a novel. I once had about 5 minutes with a famous agent who, when I asked a question about whether a book I had in mind was adult or young adult fiction, asked me, "Why are you asking that question? Just finish the book!"