Although most people only keep track of their current best, I've found it helpful to record every improvement for each skill that I'd like to accomplish.
Basically, I make a list of all the important tricks I want to work on for the year. Then I write down how many throws of that trick I would like to be able to do. I also write down what my current best is for each trick at the time the list is compiled. I put all this information into a nice spreadsheet and leave lots of room on the side for me to fill in my progress for each goal as I improve. For each improvement I write down the new record and the date.
There are other things that can be helpful additions to the list. I have a comments column to give my self ideas for things to concentrate on when practicing the corresponding trick. I also added a column for the percentage that I'm at so I can see which goals I'm closer to accomplishing, and which I haven't worked on enough. You can add your own columns to this list and you can also format the spreadsheet to your own organizational structure.
There are quite a few benefits to making this goal list:
There are a couple more important things that should also be mentioned about this goal list. First, I don't list every single trick that I work on. It is mostly endurance skills and fairly standard technical tricks. It isn't appropriate to list artistic moves since they generally aren't mastered in a long-term progression. It is important to note, though, that strengthening your technical skills definitely opens up possibilities for artistic moves.
Also, it is very important to set high goals for yourself. Goal setting must be a challenge, otherwise what's the point? As a matter of fact, from what I've seen of my and other peoples' juggling goals, generally we only achieve about 40% or less of the goals we set for ourselves each year (especially for people at higher skill levels). Although a majority of goals aren't met, most of the tricks have improved tremendously during the year. Another important factor about the unattained goals is that although something was put on the list at the beginning of the year, sometimes the trick just isn't interesting enough to be practiced through the year. It's very important at the beginning of the year that you push yourself, but it is also important to be realistic so you don't frustrate yourself with unattainable goals.
Although this whole idea sounds a bit compulsive to many of you, I can attest to its effectiveness.
I have a super-compulsive spreadsheet system set up to track my progress: goals.xls (Right click and Save Target As...)