On Beginnings...

Kathleen Dalton Woodbury gave this advice on where, exactly, one should start their story:

...the story should start when something starts to happen, and that's usually when the main character gets involved.

So, if you wanted to start with a fight scene, for example, you wouldn't start with the first punch. You'd start with the main character minding his own business, when some idiot comes up and tries to pick a fight with him. Of course, the main character, being smarter than to want to get into a fight with some stranger, tries to defuse the situation (and provides the author with a chance to do some characterization and get the reader to care about the main character), but when the idiot goes ahead and throws the first punch, the fight can start and the reader is more likely to be hooked.

Probably one of the main reasons for flashbacks is to try to show the reader why the main character is in the opening situation in the first place. If that "why" is at all interesting, the author should consider starting the story with it instead of starting it later.

One of the biggest problems with flashbacks is that they tend to stop the current story action (which, if the author has hooked the readers into caring, the readers are not going to want to have stopped) while the story goes back in time.

You don't EVER want to stop your readers as they are reading, because they may decide not to start up again.