Do a big (or especially difficult) task first thing in the morning when you’re most focussed and leave smaller tasks until later in the day.
Don’t multi-task. Focus on one thing at a time and get it done well.
Have a rule that you only touch a task once. If you open an email, deal with it then. If you pick up a piece of paper, do what needs to be done at the time. Don’t ever put it back on the pile. By dealing with that email or file right then, you’re not wasting time re-familiarising yourself with the task later on.
Have set times when you clear your emails. The first time for the day might be at 10am, and then maybe after lunch, and then at afternoon tea. Emails can be very distracting and time-consuming.
Welcome feedback! Make sure to be open when it comes to performance, a situation, each other’s role, processes, and other things. Strong relationships are built on openness and honesty. A lot of people are afraid of giving and receiving feedback, even a lot of executives and assistants. But your executive can’t change something if he or she doesn’t know what to change. Feedback is important! So, take time to give feedback, and don’t forget to ask for feedback as well.