There is no one right or wrong way to structure an account. Each business is unique with different advertising goals, budgets, and priorities. An account structure that works for one advertiser may not work for another. Ultimately, proper account structure with intuitively labeled campaigns will simplify account management and analysis, and will help you to properly test and optimize.
Review your website's sitemap to determine if you can re-use it for AdWords. Many advertisers choose to structure their campaigns according to their website's layout. You have probably structured your website carefully by topics or product, and you'll have landing pages to reflect these categories that you can use for your campaigns and ad groups.
Decide if you'd like to advertise on search, display, or on both networks.