In Steven Pressfield's The War of Art he quotes the principle of priority that states:

A) You must know the difference between what's urgent and what's important, and:

B) You must do what's important first.

This is a principle I try to follow. Not only does it help remind you of your mission, it reminds you that it should always remain your highest priority.

I often get bogged down doing things that come up, and sometimes they take over the time I should be dedicating to what I really want to do.

I have a simple rule though; if I don't have enough time to swim at least twice a week, it means I am too busy.

This gives me a good indicator of whether I am prioritising what is important to me. It's important for me to swim because it helps me relieve stress, and also keeps me fit and healthy (at least I think so), but it also means that I'm not putting other things in front of my top priorities. I still wish I could do a better job at that though.