I assume the question is asking for principles that are literally applied within the disciplines not proverbs like "measure twice, cut once" (which isn't really a principle in tailoring)

1. "Premature optimization is the root of all evil" -- Knuth, computer science
2. "Follow the information" or "what are the primitive random variables?" -- information theory, control theory, statistics
3. Procrastination principle: “Most problems confronting a network can be solved later by others… don’t do anything that can be done later by users.” (an idea from a 1984 paper by Clark, David Reed and Jerry Saltzer).
4. Never design a law with the worst case in mind -- law/legislation
5. Release early and often -- software engineering
6. Think aspirin, not vitamins -- marketing
7. Start with the simplest problem that you don't know how to solve -- general advice in technical PhDs
8. Start with a contradiction: "X but also Y" where X and Y are in conflict: many artistic fields such as script writing (this is a useful method for creating character-driven plots, by defining the central tension that drives a character for example)