You can learn a fair amount by reviewing ratified contracts. They are especially helpful for novices when it comes to formatting, clause considerations and sample language.
Bloomberg's Precedent database provides access to over 800,000 documents used in actual transactions. Bloomberg makes them searchable in a number of different ways, including type of deal, clause language, governing law, sector, parties and law firms involved. The documents are sourced from SEC filings.
A Manual of Style for Contract Drafting by 
Contract Drafting: Powerful Prose in Contract Drafting by 
Contract Law from a Drafting Perspective--An Introduction to Contract Drafting for Law Students by 
Working with contracts : what law school doesn't teach you by Note, both Westlaw and Lexis have robust model forms collections online and in their print publications. Many will contain drafting guidance from experienced practitioners.
