Plan your MBA program so that one class "builds" on top of the other. By creating a foundation, you can seamlessly incorporate the work you're doing now into a doctoral program. Even it you don't continue, it is good to have options.
Study the course outlines for all the classes you are going to take. Mark the due dates of each assignment in a glance-at-a-week calendar. At the end of each day record the number of hours you spend attending classes, reading and working on assignments.
Take copious notes of everything you read. Avoid the pitfall of trying to remember where you read something six months ago that is a perfect quote for the paper you are writing now. No matter if you use a computer file or write it in a journal, develop a system where you can easily find notes and quotations.
Develop the habit of starting papers and assignments well in advance. Jot down ideas and possible sub-sections as you think of them. When you go to write, the process of passively thinking about it--almost subconsciously--will make it much easier to complete the assignment.
Commiserate with others. Studying and student complaining love like-minded company, so make friends with the people who are also working on an MBA and share resources and ideas and edit work for each other.
Stay focused on the finish-by date you established at the beginning of the program. Avoid dropping classes--unless absolutely necessary--or handing assignments in late as this will detract from your goal.
Project a reward for yourself when you finish your MBA. Thinking about the new car you are going to buy or the round-the-world trip you are going to take will help get you through patches when you are burning the midnight oil and want to chuck it in.