Some authors say that they add a little bit of themselves into their work, I tend to agree with that as I myself do the same. A few of my characters have a little bit of myself as well as their own qualities. In a way I think this helps build that character because you the author know that specific quality as it is a part of yourself. One of my characters is an avid runner. Before I injured my back I was an avid runner. I use this specific quality not only because I know it well, but it also becomes an important part of who she becomes later on in the series (yes, I have at least 3 books that will be in this story-line).
Another character in my novel is a die-hard fan of classic movies. I took this quality from myself. I love classic movies, Cary Grant, John Wayne, Burt Lancaster, Spencer Tracy, James Cagney, Humphrey Bogart. I love Gene Kelly more than I do Fred Astaire. I have a huge collection of Humphrey Bogart movies and a huge crush too. I also have Bela Legosi’s Dracula and several other Dracula movies; I love old horror films. I could leave the TV on TCM all day and be completely satisfied, but our network doesn’t pick it up.
Not all of my characters have all or part of my qualities though. Most of my characters are their own uniqueness. I enjoy creating each one of them. At first I had to write a list to tell me who is who and who does what, but after a while I get to know them really well.