Hi! I need your help!

When I was a schoolgirl all teachers of English insisted that you should say 'help to': I must help my mother to cook the dinner. But now I often see 'help' without 'to': Strategies to Help Prepare Students for Group Work. So which way should I use it, with or without 'to'?
Oxford English Dictionary says as follows;

Previously only 'help someone to do' was the form used in formal writings. But since 16 century on, 'help someone do' has been used in colloquial speech, and now this form is also accepted as formal.
Thank you!