I'm a new builder, so every task is met with trepidation and excitement, usually followed by frustration and disappointment....
There was a vote earlier for "fixing my mistakes." That would be my first vote, except that I find fixing my mistakes to be satisfying as well as a learning experience, and I think it is a necessary skill.
So, my vote is for cleaning up and polishing brass castings as well as locks. Seems to take forever, I have no technique or skill at it, and generally think I take 3 times as long as it should. Nothing is worse then knowing you must be doing it wrong...
Cheers,
Chowmi