The most important thing you have to complete is to set priorities for your tasks and to force yourself to follow them.
You have to work not harder, but smarter. You have to follow this rule: 20% of tasks give 80% of results.
A famous management expert, Peter Drucker, says "doing the right thing is more important than doing things right." Doing the right thing is effectiveness; doing things right is efficiency. Focus first on effectiveness (identifying what is the right thing to do), then concentrate on efficiency (doing it right).
Actually, it is hard to set priorities in real life. Personal Motivation Calendar will help you.
Personal Motivation Calendar allows you to divide all tasks into four categories using two criteria - importance and urgency. This technique known as "Time Management Matrix" was developed by Dwight Eisenhower and described in detail by Steven Covey, the author of a very popular book titled "The 7 Habits of Highly Effective People".
You have to enter all your tasks into the Personal Motivation Calendar tasks pane according to their importance and urgency at the same time.
Let's take an example.
Let's imagine you have the following tasks (some of them are your wishes and plans delayed for future):
- Help a colleague with the computer
- Review news sites
- Make a presentation on the new product
- Prepare a report requested by the boss
- Learn Chinese
- Open a personal blog
- Learn the speed text typing technique
Some of these tasks are more important for you, some are less important. Some of them have to be done "for yesterday", some of them can wait.
Let's enter these tasks into a table with four categories (1 - high importance and high urgency, 2 - high importance and low urgency, 3 - low importance and high urgency, 4 - low importance and low urgency).
The following picture shows the tasks entered into the Personal Motivation Calendar Tasks Pane:

Tasks have to be done starting from the 1st category and finishing with the 4th category:

In each category tasks have to be ordered from the most important ones to less important ones (from top to bottom):
After entering the tasks into Time Management Matrix, we can easily see the order in which you have to work on tasks:
1. Make a presentation on the new product
2. Prepare a report requested by the boss
3. Learn Chinese
4. Open a personal blog
5. Learn the speed text typing technique
6. Help a colleague with the computer
7. Review news sites
You have to remember that tasks are not static - you can change the category and the importance order in each category depending on current value of tasks for you. Use the mouse to drag and drop tasks between categories and reorder them in each list.

It is very important to follow the rule that the most important tasks have to be done first. People easily confuse importance and urgency. Always remember that importance and urgency are not the same. Importance always has a higher priority. But urgent tasks can be tasks that are valuable not for you, but for somebody else who persuades you to complete them.
And any time you are going to do something (or are not going to do anything), ask Lakein's Question, "What is the best use of your time right now?"