"Be specific" is a nice flinch, I've always had it and it helps a lot. "Don't moralize" is a flinch I learned from experience and it also helps. Here's some other nice flinches I have:

1. "Don't wait." Waiting for something always takes more time than I thought it would, so whenever I notice myself waiting, I switch to doing something useful in the meanwhile and push the waiting task into the background. Installing the habit took a little bit of effort, but by now it's automatic.

2. "Don't hesitate." With some effort I got a working version of this flinch for tasks like programming, drawing or physical exercise. If something looks like it would make a good code fix or a good sketch, do it immediately. Would be nice to have this behavior for all other tasks too, but the change would take a lot of effort and I'm hesitating about it (ahem).

3. "Don't take on debt." Anything that looks even vaguely similar to debt, I instinctively run away from it. Had this flinch since as far as I can remember. In fact I don't remember ever owing >100$ to anyone. So far it's served me well.