I'd disagree with cgod and say to start with Yojimbo/Sanjuro. I love Seven Samurai, but the length can be quite a commitment (210 minutes). Yojimbo on the other hand is an easy 110 minutes I think. Plus, it's very accessible if you've already seen A Fistful of Dollars.
Oh yeah. I mean it's a toss up really. Just think Yojimbo is only a tad easier since it's so much shorter. Both are great
It's between Yojumbo and Seven. I shall flip a coin and report back. I am excited to discover a "new" director. I've heard him mentioned for years.
You may also consider "Rashomon!" It's a very interesting take on reliable narration and has a phenomenal performance from Mifune (and everyone else, really), plus it's only 1h23 min :D But as the others have said, any film of his is a great place to start