If you want something done, ask a busy person to do it. The more things you do, the more you can do.
I feel like when I am at my busiest I am also at my best. When my boss hasn't quite given me enough work and I know I will have plenty of time to complete tasks, that is when I get distracted easily and carried into other things... for better or worse...
However, for me to manage those times when the plate is crammed a little too high and I start to feel stressed out, I like to do a prioritizing exercise I will call the "Important/Urgent" Matrix. I use a white board and draw a grid that looks a little like the image to the left (minus the reminders within each box).
I usually take sticky notes and write out each and every task that is on my plate. Sometimes I do this exclusively for work, but often it is a bit of everything that is weighing on my mind and needs to be documented. Once all my stickies are in a stack, I start putting them on the matrix according to how urgent they are (due today or in 3 months?) and how Important they are (will this make/break my career or is very important to a client/boss etc, or just a "Nice to have" I will get to if I have time?)
For example, reporting my hours each week on Friday AM is not extremely important, however it is due on Friday and therefore urgent. Completing my ethics training is important and required for me to keep my job, but it is not due until the end of May (thus important and not urgent).
From this exercise, I walk away with a "plan of attack" and feel a lot more capable of achieving the tasks ahead of me. The ones I immediately take off the white board and start plowing through are the Urgent and Important (and I try to do them in the order of highest urgency/importance). I typically don't have the luxury of delegating the ones in quadrant 3 so I have to do those first and then quadrant 2 and 4. However -- even if I don't go through each of the exercises or complete each of the tasks in all quadrants, the practice of taking a step back, reviewing everything to do and prioritizing is really renewing and calming for me.
How do you manage everything when your plate is a little too full?