Some time management gurus tell us an "A" task on a list of things to do is something that has a high reward for getting completed--and carries a big consequence for not getting done. You know, like filing your taxes--the possible reward of a refund if you get them done, and the reality of nasty penalties if your taxes aren't filed by a specific date. (This blog is not suggesting that you skip this annual ritual.)
While this approach to managing activities can get you through a crisis, using this mantra as a model sets you up to allow your problems to determine your priorities. Whatever is loudest and carries the biggest threat becomes the primary focus of your energy and time. A large, demanding client company consumes huge amounts of time and resources (usually at lower margins) while easier, more profitable clients that might eventually become large customers quietly go away due to your lack of availability.
If your world is driven by noisy, demanding problems you have a bigger problem than the one you label "time management." When your problems determine your priorities you can be sure whatever you're trying to solve isn't the source of your problems.