Asking somebody’s opinion:
http://www.ihbristol.com/useful-english-expressions/example/asking-somebodys-opinion/6

Politely asking someone to do something:
http://www.oneworldofenglish.com/english_grammar_reference/politely_asking_someone_to_do_something.htm
http://www.oneworldofenglish.com/english_grammar_exercises/fawlty_towers_polite_expressions.htm

How to give advicehttp://www.engvid.com/polite-english-giving-advice/#quiz