First the advice: Don't try to write his dialect if you don't know it inside and out. (I grew up in rural England and have certain areas very much in my ear.) If you attempt it, don't try to spell out the accent. Just use word order and an occasional contraction to indicate it. Keep his speech simple and straightforward, but not stupid. (i.e., follow lillybaggins's guidelines about not dumbing him down.) He is a hobbit who'd like to live up to his potential, not to be less than he can be.

Some points I bear in mind when I write him: Sam works from love. Love of family, of the Shire, of all things that live and grow (except maybe Shelob and the Orcs), and, of course, Frodo. (And I don't mean that in the slashy sense, much though I love it that way.) He wears his heart on his sleeve, but he's also guarded when he needs to be. His emotions are close to the surface in a lot of ways, and he is much slower to anger than movie!Sam. He is honest and forthright (except when conspiring against Frodo fro his own good), though shy at times, and is largely unaffected by the Ring because it has nothing he wants, and its evil cannot understand him. He's had harsh words from his Gaffer, whom I don't see as a bad person, but as one who has accepted more limitations than Sam and is comfortable with them in a way that Sam could never be. Sam is both intelligent and very strong, deep down, though many underestimate him at first blush.

A prompt: "Well, now, my Gaffer's the one to ask about them taters, Mr. Frodo. He knows more about root crops than anyone else in the Shire, begging your pardon."

Hope some of this helps, and thanks for letting me ramble about a favourite subject! :)

Catherine