One of the (seemingly) simplest is this: say NO.
There are some rules, of course! These are the ones that work for me:
When I am overwhelmed
Duh!! Though this is such a no-brainer, I find most people struggle with it. The trouble often is that people aren't aware of their 'real workload' as opposed to their 'perceived workload'. There are several ways to differentiate, but that's another post! The thumb rule is, if the thought of the new task causes a spike in your heart rate and blood pressure, or you experience the starting of a panic attack, turn it down! :) Seriously, if you think you can't manage it, you're already on the losing side, and it turns into a self-fulfilling prophecy very quickly.When I am not suited for the job
Once again, this is something a lot of people have a lot of difficulty with. Most people labor under the misapprehension that employers will label them lazy for turning down 'challenging' tasks. First: a task that you are not 'suited' to is not 'challenging', its something you 'might just be able to pull off, with a little help from person x and y'. If that is the case, you will be biting off more than you can chew, especially if you have other tasks that are challenging (in the true sense). Second: Most employers will value your honesty, and allow you a more natural learning curve, organise training, etc. Learning on the job should not happen at the cost of the task at hand.When someone else is much better suited for the job
This one is a winner - it has several benefits, especially if you volunteer to assist: a) It does not add to your workload (yay!); b) The job is performed more efficiently; c) You get to observe, learn and adopt better practices; d) Adds to the teamwork quotient in the office. The last two benefits, in my experience, are the most important. The simple act of acknowledging another person's supremacy in a particular domain goes a long way in setting a positive tone for the relationship to evolve, thus facilitating greater learning. Win-win! :)
There are several other, smaller reasons that also deserve a mention - when the task doesnt interest me at all (I tend to drag my feet), or goes against the grain of my beliefs (subconcious sabotage). I use these reasons very sparingly, and after a lot of thought. The top 3 however, are no-brainers.
Remember that our limitations are real concepts - in our heads. If you think you can't do something, or that you don't have the time, or the mental juice to take on a task or carry it through to completion... then don't, because you've doomed it at the very beginning.
There are lots of ways, of course, to reprogram our thinking (which often tends to the negative) around what we consider boring/pesky/petty tasks. More on that soon. :)