One of the best ways to make sure that you are completing the tasks you need to is to record them somewhere. A handwritten day planner or a digital one, such as on a phone or computer, will do. The planner should be in the same place in your home every day, and have space for you to keep daily schedules for immediate tasks and monthly schedules for longer-term tasks. Get in the habit of referring to it three times a day to make sure you're on track to complete your work.
Once a month, write down in your planner any goals you have for the whole month. They can be quantitative goals such as "finish work project," or regularly occurring ones such as "go to the gym once a week." Once a week, refer to your monthly goals and write down any weekly goals that will help you reach your monthly goals. Once a day, refer to the monthly and weekly goals and see whether there are any daily tasks that will help you reach those goals.
Rather than trying to force yourself to do all of a long task at once, use a timer to set smaller time goals. For example, if one of your goals is to read a report for work, set a timer for 20 minutes and commit to filling that 20 minutes with reading. When the time is up, take a break. Set another timer for 10 minutes to do other things, then come back to the reading for another chunk of time.
Set your phone to silent and turn off e-mail alerts on your computer. Decide on specific times to check your e-mail or voice mail and leave your phone and computer silent except for those times. Restrict other activities that interfere with your ability to focus, such as spending long periods in front of the television.
If you find that you are spending lots of time trying to figure out tasks that you are not good at, try delegating those tasks to another person. For example, if you are meant to make weekly schedules at work, but you have a hard time with your scheduling program, speak with your supervisor to see if you can share that duty with someone else. You may find that another employee is not good at something that comes more easily for you.