I love the brainstorming part of writing. I usually have a basic premise in mind and then I talk to friends and they suggest things that could happen.
For example, in my current work in progress. I have a victim based on a former boss. This was an idea I got right after he was fired from the company I used to work for. No one like the guy as he was a pompous horses patoot. My husbands supervisor and our good friend Joanne lightly suggested that I use him as a victim. We decided that he was going to die horribly as revenge for the bad way he treated everyone who worked for him. I am not giving away any more secrets so stay tuned. There was a lot of brainstorming as to how Dennis was going to croak. I also brainstorm ideas with my editor. She had a particular request to name one of the annoying characters in the book after someone equally annoying that she knows. Having heard Stella stories over the past few years I knew just how my character would be.
Plots are fun to brainstorm as well as the characters. As most of my mysteries are pretty quirky I have a great time writing them. I take stories from other people (with their permission of course) and use them. In fact someone even double-dog dared me to use a particular anecdote in the book. I was able to do so as it fit with my lead characters line of work. I like talking to people about brainstorming ideas for my work as they are the ones reading the stuff. The more heads the better.