Requesting something to be done for me in cantonese
First you say "would you please", which is "唔該"(please/ excuse me- more colloquial) or "請你" (would you please- more literary); you can even say "唔該" and "請你" together and say "唔該請你" (excuse me, would you please)
then you say "help me/ for me", which is "幫我" or "同我"
then you state your request. 


For example: "打開度門" (open the door)

The whole sentence would be: 

"唔該幫我打開度門" or  "請你同我打開度門"

You can substitute "打開度門" with any request

To be extra polite you can replace "請你" with "麻煩你/ 勞煩你" (trouble yourself)

If it was a command, you can just state your request directly. e,g. "打開度門!" or simply "開門!" 

Cantonese use final particle much more often than Mandarin. The most native way to say it, is "唔該幫我打開度門吖" -- using final particle '吖' to soften the tone and make it sound less demanding