First:
Watch the original, original Star Wars (1977). You’ll want to watch some fan edit online, like Harmy’s De-Specialized edition or something that you can find via this website.

Second:
Watch the original, original Empire Strikes Back (1980). Again, you’ll want to watch one of the de-specialized fan edits online.

Third:
Watch the original, original Return of the Jedi (1983). As always, you’ll want to watch one of the de-specialized fan edits online.

Do yourself a favor and don’t ever watch the prequels period. They are terrible movies that will one day thankfully no longer be extant. The originals, on the other hand, may very well live on to be shown one day in a galaxy far, far away.