Ask direct questions, don't be afraid to ask dirctly if they want to kill or hurt themselves.
Get professional help; even if the person resists.
Remove means (dangerous objects of self-injury) from household; pills, firearms, knives, etc.
"Would you like me to get you help?"
"Are you feeling like hurting yourself?"
"Do you have a plan?"
"You're just trying to get attention."
"You have to pull yourself up by your boot-straps."