How to Make Requests That People Say Yes To

English encodes politeness in structure. The longer and more indirect the request, generally the more polite it reads.

The scale

"Send me the file." — an instruction. Fine downward, or in emergencies.
"Can you send me the file?" — direct, casual, fine with peers.
"Could you send me the file?" — the safe default almost anywhere.
"Would you mind sending me the file?" — noticeably polite.
"I was wondering if you might be able to send me the file." — very polite, or for a big favour.

Level five for a small favour sounds strange. Match the length of the request to the size of the ask.

Add a softener

"…when you get a chance."
"…if you have a minute."
"…no rush."

These signal you are not demanding immediate action, which makes agreement easier.

Asking for a bigger favour

Acknowledge the size of it.

"I know this is a big ask, but…"
"Feel free to say no, but I wondered whether…"
"Would it be a huge imposition if…"

Explicitly giving permission to refuse makes people more likely to agree, not less.

Answering "would you mind"

This one confuses learners. "Would you mind waiting?" — "No" means you will wait. To be safe, answer with words rather than yes or no: "Not at all" or "Of course, no problem."