Wow congrats on the half marathon 2 years ago. You clearly have the capability to achieve. Set your goals (modestly) and get someone you trust to help you build a workout plan.
I am not sure what your fitness level is....however, generally start slow and pace yourself. If you start with a walk, it will become a power walk, which will become a jog or run later.
How do you like to workout? At home? A gym?
I find variety is best. But we are all different.
Don't be hard on yourself....take it one day and one step at a time.
Weight Jan 1, 2011 = 288 pounds (size 24)
Weight April 1, 2011 = 244 pounds
Weight July 1, 2011 = 220 pounds
Weight September 22, 2011 = 203
Weight Goal April 6, 2012 = 185 pounds
Ultimate weight goal = 155 pounds Sept 1, 2012
Current Weight = 213 lbs (size 14)
Total loss to date = 75 lbs