The thread that alaskayorkie linked has an AWESOME tutorial! That's how I learned to do the topknot. I was doing it all wrong until I saw that! Here it is:
Topknots shared by Linda Grimm and Maria Lelinho starring Rocky! Many Thanks!
How old is your baby? I only do Uni's topknot for special occasions bc she doesn't have a lot of hair. for everyday I just use mini barrettes. You have to train them to hold still. Brush her several times a day, and teach the stay or freeze command. If you keep doing it all the time, they will just accept it is a part of yorkie life.