It is important to understand the difference between sweepstakes and contests in order to maximize your chances of winning.
Contests - Usually require some sort of skill beyond simply submitting an entry via mail, online or via Facebook or Twitter. The types of contests vary and include the following:
Essay Type Contests - These types of contests require the entrant to prepare an essay addressing a particular subject of interest to the sponsor or promoter. Some are quite simple and limited to 50 characters while others may require essays up to 1,500 words. By definition and stated within the rules for the particular contest, the judging factors will be stated including originality if applicable, clarity and will state when internet voting is an integral part of determining the winner. Compared to sweepstakes, essay contests will usually receive fewer entries and therefore the odds of winning are better. Some essay contests allow only single entries per household while others may allow multiple entries. It is important to assure grammar and spelling are checked before submission.
Puzzle Type Contests - While less frequently seen and depending on the difficulty of the puzzle, the odds of winning a particular contest may be increased.
Prediction Type Contests - Prediction types of contests are more common and usually involve sports predictions and/or fantasy team submissions. While the number of entrants may be siginicantly less than other contests, the entrants are typically skilled at these types of predictions so unless you're a sports pro, you may want to invest your time in a contest where you have the skills required to improve success.
Sweepstakes - Sweepstakes by definition in most of the United States are those that require no special skills other than data entry to submit requested information to be contacted in the event you are selected as a prize winner.
Cash Sweepstakes - Perhaps the most popular type of sweepstakes and usually attract the highest number of entrants.
Instant Win Sweepstakes - Again, very popular due to the instant gratification of being selected as a winner. Prize value vary greatly but generally are of lower value and usually there is a grand prize that all entrants become eligible for.