Contacting and sending Game Developers Feedback

How does one exactly go about doing this.

I have read many articles that state developers choose to implement certain characters or features in a game because of fan feedback. How are these fans reaching game developers exactly and how do they sound constructive without sounding buggy and annoying.

Thank You

Most likely through the developer's forums (or forums like this, even). Almost every developer these days has one on their Web site. That or they're getting feedback via e-mail. The former seems the most likely, however.