There are two common phrases we use. 1. Help!! - ช่วยด้วย Use this word when you have an accident or you were robbed. I always hear people say this word very loud to show their emotion. 2. I need some help. or Help me please. - ช่วยผมด้วย This sentence sound more calm and you don't need urgent help. Example sentence in English is "I lost my way, help me please." or "I want to go to the zoo, how can I get there?". These are explanation from your sample. อุบัติเหตุ - accident (what context would this be used in?) I might be confused if you have an accident or you see someone has an accident. ความช่วยเหลือ - assistance/help? You should say "ขอความช่วยเหลือ". Even it sounds unusual for me but it's understandable. ผมได้รับบาดเจ็บ - I am hurt This is understandable for me. But it sounds a little unusual. กรุณา - please This doesn't make sense if you just say "กรุณา". I feel like you want some money for me. :) ผมต้องการ - I need... You can say this word but please say what you need. If you just say "I need ..." I will think you want to have sex. ผมต้องการความช่วยเหลือ - I need help This is very formal way to ask for help in Thailand. Too formal.

ช่วยด้วย !! - Help me!!!

all you mentioned is not considered too formal. ofcourse you can use it when you need help, or when you call to the police. but, if you really need help from people around at the moment you just need to say ช่วยด้วย ช่วยด้วย ช่วยด้วย is far enough