It depends on the situation . 

If somebody is trying to steal your wallet then no one is going to think you are rude for not saying please when calling for help .On the other hand if you are at work and you need some help then it would be considered rude not to use manners when asking for help . 

Uk perspective but i assume it is going to be similar in most countries .

For US English: 

Could/Would you (please) help me with this? (please can be used but it isn't rude to leave it out because you use could/would and a question form to make it polite)

Please help me with this. ("please"is necessary here, as it transforms the sentence into a request. Without "please" it is a demand, and should only be used as the other commenter said, when you are in a situation requiring immediate action)

Will you (please) help me with this? (can sound rude depending on your tone without "please" so I think would/could is better than will, 

I am looking for someone to help me improve my English. (please is not necessary)

Thank you for your specific explanations, merlyn. I didn't expect the punctuation and interrogation were so important before, now I get it .

@Sarah

Yes, you should always say "Please correct me/tell me your thoughts"

Saying just "Correct me." is impolite.

"Is this correct?" "What are your thoughts?" are also okey, but notice they are in question form not command form.

If it is a Notebook or Answer entry on this site and you don't have space, it is better to just say "Correct?" 

Others tips:

use just ONE question mark because otherwise it makes it look like you are angry and shouting at someone. 

Don't use an exclamation point (for the same reason)

Thank you merlyn, if I want to ask a question, is it a proper way to say :please tell me about your thoughts or please correct me? Many people on italki didn't use please when they asked a question, the only reason I think just like me that we didn't realize it was a rude behavior.