I have ADD, and staying on task is hard. Here’s a few things that help:
1. Keep projects to a minimum; learn to say no, don’t start things impulsively.
2. Minimize cluttter. It’s easier to be productive when things are neat and orderly.
3. Spend time organizing how you’re going to do something when you first get an assignment, and break the work down into small, manageable tasks. For example, “clean the living room” may be daunting when you look at the clutter, but 1. pick up the newspapers and put in the recycle box 2. Put all the dishes in the dishwasher 3. Put videos in a bag near the door to take back 4) take all shoes into the bedroom and put them in the closet, and so forth is much more doable. Likewise for school and work assignments. Take some time as soon as you get an assignment to plan out what you need to do in small pieces of work, and when you need to have each piece finished.
4. Make lists of what needs to be done, and cross things off.