Don't waiver when drunk, in a really bad mood or overworked IS very good advice. My consistent error is forgetting, when fed up with a pitcher, to check to see if they are already listed as the next starter and already WWing another player needed to meet the cost of WWing the pitcher and getting a better one.
At which point I realize that the guy I wanted is going to be gone by the time the next start is over AND I have lost the bench player or reliever who deserved better, sacrificed in vain.
I use the team notes to remind myself of when so-and-so is starting, when I have left an AAA er in the rotation after an emergency start, or a regular player in AAA - usually I have small letter notes, but when it is one of these situations I write URGENT !! and then an all-caps note to myself to remember and at what point. Can't always check these in time, but it has reduced my stupid mistakes to a manageable level.