Tidy up at the end of each day
Set aside 10 minutes each day before finishing to organise my desk.
It sounds easy, but personally, it's still a difficult habit. At the end of most days, my head is rather frazzled and disorganized to remember this to do so. Also, when dealing with cleanups with computer tasks, it's easy to get distracted and forget about what to clean, when to stop and pack up.
In addition, stopping is not a fixed time where I can anchor the behaviour to a wall-clock time - it's typically very possible to end up working so late that it's easy to bypass this habit and head straight off home.
However, it shouldn't be such a difficult thing to do, and in fact it shouldn't take me no more than 5 minutes.
I should also make a checklist of what to do for cleaning up at the end of the day. That way I won't forget or have to expend more mental energy to remember what needs to be done.