Automation. My number one thing might be learning to use multiple cursors in Sublime, I probably jump into it 10 times a day to psuedo-automate text editing. I wrote of one example here: http://jontelang.com/blog/2016/06/22/sublime-efficiency.html

Another thing is, also automation, to use Hazel to automatically keep my temp files manageable. Basically, when I file is older than X days, move it to a "need review" folder. This mean that there is a steady but very very manageable flow of files to delete or move to their correct location. I also wrote about it here: http://jontelang.com/blog/2015/08/17/hazel-is-great.html. My Downloads folder have not been 1000s of files since I started with this.