You can choose one large task or multiple small tasks. As long as you are willing to give your undivided attention to the tasks. Preferably in sequential order.

Make sure to focus on the tasks you've listed. It's very important to keep this time distraction free. Whether that be from your phone, email, or other people.

After a successful Pomodoro check off any completed tasks. This may seem like a small step, but it creates a feeling of accomplishment. Which is vital to productivity.

Do whatever you feel like during this time away from your work. This will give your brain a rest which thus preparing you for the next Pomodoro.

The steps up until this point aren't truly effective unless they are repeated multiple times. Once a pattern is created the true power of this technique is revealed.

Even with the shorter breaks your brain can still get bogged down with whatever tasks you are working on. Make this time truly restful and mindless.