When flying IFR, working with ATC is a partnership. You and your controllers work together as a team to get you safely from A to B. Most controllers will do everything they can to move you through the ATC system as efficiently as possible, give the current weather and traffic situation. Their will be times when you may have a specific requirement that the controller could not anticipate.
The following is a collection of articles an audio episode that will help you get what you need from ATC; and explain why ATC cannot always accommodate your request for a change your route, altitude, or airspeed.