My favorite workflow:
1. Negotiating about everything important for both, client and me;
2. If possible having a nice Skype interview, exchanging ideas and views and making final agreement;
3. Making first sketches and getting first reviews and approvals;
4. Getting first milestone;
5. Finalizing the project.
Bottom line, I firmly believe both sides should trust each other and offer things that will strengthen that trust. Specially when collaborating for the first time.
Two things I really don't like are:
1. Asking for money in advance without showing at least a preliminary sketch
2. Being asked to work without getting any advanced payment.
People should know we artists have to eat and get some nice treats as well as other people :)