Study the kind of metal you like by learning theory and looking at the tabs/music there is available out there.

Once you get that it's just the physical process you need to get under your fingers and that's no different from any other kind of learning; read the stickies.
R.I.P. My Signature. Lost to us in the great Signature Massacre of 2014.

Quote by Master Foo
“A man who mistakes secrets for knowledge is like a man who, seeking light, hugs a candle so closely that he smothers it and burns his hand.”

Speed Mechanics for Lead Guitar by Troy Stetina is a good one. It's a kinda advanced so might not be the best thing to start off with though. He does have some other books aimed at people starting; I haven't read them, but I'd guess they're good.
I would recommend any books written by Troy Stetina where there are many of em' that you can find suited for your current level.