Answer
- Never play cards with a man called Doc
- Never eat at a place called Mom's
The original quote from his book Walk on the Wild Side has two more laws:
"But blow wise to this, buddy, blow wise to this: Never play cards with a man called Doc. Never eat at a place called Mom’s. Never sleep with a woman whose troubles are worse than your own. Never let nobody talk you into shaking another man’s jolt. And never you cop another man’s plea."
I have no idea what the actual fourth law means ("jolt?"), although there are theories.