It is always best to ease characters into your book rather than throwing them in all at once. NEVER introduce more than (arguably) three characters at a time. And that is AFTER you have established your MAIN character. I have made this mistake over and over, even within the same novel. It is of admit-able difficulty to do this--at least it has proven to be a challenge for me. And while I wish I could offer a trick to fix this, it is merely a process that I have worked on through editing time and time again.