They mean the same, but the second one is more commonly used as the "please" coming first in the sentence is considered more polite. Starting off with "Pass me the salt" sounds a little like an order

Both of these sound like commands to me. Either 'Please pass the salt' or 'Pass the salt, please' sound cold and unnatural. I can't imagine friends or family saying this around the dinner table. I'd say 'Can you pass the salt, please?' or 'Could you pass the salt, please?