i am terrible at them. i always forget. i keep a notebook at work - i just hide it somewhere inconspicuous - and every day before i leave i write down how long i worked. and then when it comes time for the timesheet i pull out my notebook.
Make it a habit ... do you submit your timesheet on paper or electronically?
I used to keep an excel version of the timesheet on my desktop. (The time invested to make it pales in comparison to the time saved by having to think about it.) Then, the habit part. Before you turn off the comp, you open the excel file, add your hours that day, takes 30 seconds and bam, you are done. And if you make a nice timesheet, it will add the columns for you and no other thinking necessary.
"Remember always that you not only have the right to be an individual, you have an obligation to be one."
― Eleanor Roosevelt
"When people see some things as beautiful,
other things become ugly.
When people see some things as good,
other things become bad."
― Lao Tzu, Tao Te Ching