1. Set yourself realistic goals. Taking on too much at once can cause unnecessary stress and worry.
2. Give yourself enough time to complete your goals.
3. Write lists.
4. Prioritize your tasks.
5. Plan your week day-by-day.
6. Group tasks together where possible.
7. Work at a steady pace.
8. Avoid distractions.

Some productive application can help you mastering Multitasking. Float It and Super Shortcuts is one of them.