Method Acting? How do actors do it and what does it take?

I have been recently practicing my acting skills. Things like going to the grocery store and being a different person. But I want to go a little further and practice my method acting. I hear about a lot of actors getting really into their charactors. I think that is great but it has also caused harm like in Heath Ledger's case. So how do you do is sucessfully? I basically just want to prepare myself so when i do meet with opportunity. I will be ready. Thanks!