There is often a lively debate on how to introduce Star Wars to a person who hasn't seen it yet.
Start with Episode IV? Episode I? Rogue One?
There are a lot of different theories
Though Machete Order (which essentially skips Episode 1) - is my favorite - check that out here. It gives a detailed account of the best order possible to preserve the story/spoilers etc
An updated Machete order blog is also up - and lives here (since a couple of movies have been released since the original). Also - see the handy graphic below