Method to handle many things at the same time is to give full focus to one thing at the time, and not letting the others to disrupt your focus. Most important thing is the capability to switch tasks. It requires skill to let one thing go and jump into another. For many this is the hard part, they can't really let the other thing ago and for that reason are not able to concentrate on the new thing either.
There is couple of tricks I use for task switching. The number one thing is, there's always time for documenting the status. It doesn't take long to write down the thoughts, ideas and place you where, when you jump in to another task. When you learn it, it takes only 5-15 seconds. With doing this, your awareness can be totally focused on the new thing. Without short documentation, you need to try to keep your previous status on mind, and you can't focus on the new thing.
Second thing is closely related to the previous. In order to be able to document your situation fast, there needs to be ways to document it available. Either it's the textpad in computer, note taker in mobile or post-it with pen, these needs to be available and you need to have a practice of documenting the status with that tool. It's easy to learn, but you can't afford 30 seconds of waiting, where to document.
There are many good methodologies on concentrating on essential. I really recommend trying out habit 3 from 7 habits of highly effective people, personal backlog, personal kanban board, pomodoro or any other time and task management system. Even though these are excellent ways to learn to use your time more efficiently, these still don't change the fact that sometimes you need to change tasks rapidly. Either it is the phone, email, text or something that comes to your mind suddenly, you still need to be ready to act on it. For that, it's best to learn to change tasks fast on the fly.
Written by +Henri Hämäläinen