Step 2: Research Schedules and Rails.
Be aware that you pretty much have to pass through downtown to get from one end of town to another if you use the T, particularly if you have to connect. The T-maps are NOT to scale! You may be able to get there faster by taking a cross town bus or biking part or all of the way.
Get acquainted with where trains go and at what times, or just use this trip planner. Look at where lines intersect (such as, you can switch from the red to green line at Park Street.) Since trains come every ten minutes at most, it would be silly to look up arrival departure times for trains. However, you should know when the trains start running in the morning and stop running at night to plan your trip. This is REALLY important if you're heading out for the night and may be decidedly less sober in a few hours, and therefore ill equipped to do any research. If all you have is cash, make sure you can use cash at your stop. Finally, the MBTA offers a T-alert system, which sends you notifications about delays of 15 minutes or more on your usual route.