Roy Hodgson walks you through the 4-3-3 formation, using Mourinho's Chelsea side as an example. Two big keys are having good wide players who like to take players on and can get crosses in, and then having a strong central midfielder who likes to stay home and defend, like Makelele.
Problems you have is getting another central player into the box when goal scoring chances come and then getting back to defend. For Chelsea, the two wide players got back for Chelsea. But choosing a system all comes down to what types of players you have and putting them in roles that make the most of their abilities.