I've recently started trying to adopt the habit of putting two spaces after every period. This was not something that I ever learned, and it's something that still seems very foreign to me to do. I've of course seen plenty of other people who do this, but it's not been anything I've ever wanted to do myself; I always thought it was an antiquated practice. But recently I've learned that it throws off page counts in Standard Format, so I'm trying to learn this as a new habit.
I'm getting pretty good at automatically remembering to add that extra space most of the time, but fairly often I look back at my text and notice a string of places that I missed. Ah well, I've taught myself to put spaces on either side of em dashes, to put spaces between my ellipses -- and then to take them out again once I learned that was wrong -- and to put spaces between parentheses and their contents in programming but not in fiction. Ah well, I'll have this latest change down soon enough, despite years of conditioning to the contrary. It's just a bit amusing to see my subconscious struggle with it for the time being. How hard or easy do you find changing habits like this to be?