Religion is sincerity
Do not feel reluctant to advise your friends, relatives and colleagues.
Do not ever be rude.
Do not advice in a rough manner or in public lest it will turn to be of un wanted outcome.
It was narrated from Abu Hurairah that the Messenger of Allah said:
"Religion is sincerity(An-Nasihah), religion is sincerity, religion is sincerity." They said; "To whom, O Messenger of Allah?" He said: "To Allah, to His Book, to His Messenger, to the imams of the Muslims and to their common folk."