I don't have ADD, but I do often have difficulty with certain tasks like charting at work (love the patient care side of things and don't have difficulty there) sending presents for out of state family, concentrating on cleaning one room in the house. Etc. Basically executive function tasks sometimes are difficult for me, but more due to my chronic fatigue I think.

So I break down the task into smaller ones and set deadlines for each task.
Take the gift example. Instead of "I need to get my niece her present by her birthday" instead of three months later.

1) Buy present 1-2 months in advance
2) Wrap present
3) Get present properly boxed up
4) take to post-office.

It might sound ridiculous but I really just get overwhelmed at the thought of getting that all done at once and feel too tired to even start. By giving myself one step at a time with specific deadlines for each I can make it happen.