Under "what useful trick/hack will save my life one day?" is this excellent tip for getting emergency help from strangers:
Learn how to ask for help against the Bystander effect:
Identify one person to directly intervene and help you: you are unlikely to know people's names in some situations involving bystander effect; next best thing is to describe such that there is no mistaking who you are pointing to ("You sir with the blond hair wearing that red sweatshirt! Please help me off the ground!")
If you can, Identify another person to call the authorities. Don't assume someone is already dialing 911. Point out the person and describe person as you see him or her such that person knows you are pointing at him/her.
The idea is to reduce the effect of diffusion of responsibility in the bystander effect, by you placing direct responsibility on specific individuals.
The way you practice this skill such that it becomes second nature and automatically engage when you are in trouble, is by practicing delegation the same way. Instead of asking a group of people to "set up a room" for example, be specific: "John, can you please set up the tables? Barbara, can you take out the decorations and start hanging up those up on the wall over there?" etc.