In all emergencies, remaining calm is key!
The first instance, help is required.
You can call for help at any time on 999, including using phones with no credit or even a sim card.
Even better, Phone 112
This number works alongside other emergency numbers in over 94 countries worldwide (including China, USA, Australia, Europe, etc). The operators can speak several languages, English and French among them.
112 is also useful as it also can be texted to for help. Users have to register for this service. To do this text 'register' to 112 and then text 'yes' to 999. Useful for first aid or security emergencies in areas of poor mobile phone coverage!
There are situations where calling for help normally is not possible, and the person calling is unable to talk. If this is the case, let the operator know! Press 55 on your phone after calling 999 or 112 - that will let the operator know you are unable to talk.
Alternately, you can text for help to 112 as above!
Give an exact location
Letting emergency services know where to go - use an address, or What3Words (free app for all phones!). What3Words describes locations using a unique combination of three words. Emergency services are happy to use this too!