I spend a lot of time avoiding stereotypes. Blondes are not always dumb. Computer geniuses and scientists are not always geeks. Heroes aren’t McGuiver and don’t always have the answers to any question or situation they confront. Heroines aren’t golden-haired princesses who have birds and fairy dust floating around them as they do no wrong. Moms and dads aren’t the Cleavers. Gay men aren’t uber-feminine. The bad guy isn’t always evilest evil who ever existed.
Stereotypes for characters can go on and on. Let’s face it stereotypes are easy to write. Many of us spend a lot of time doing character-building for our main characters—at least, we had better be doing this. But what happens when we have to write the next door neighbour or the gas station attendant or a cop? We fall back on stereotypes. We have preconceived notions of how these people should/will act. This is one of the trickiest places in a manuscript. My suggestion for this is to do a small sketch for this characters. Not a lot. A half page. All characters are important. Don’t let the secondaries take over the book, but don’t neglect them, either.