The most effective debugging tool is still careful thought, coupled with judiciously placed print statements.

Do what you think is interesting, do something that you think is fun and worthwhile, because otherwise you won't do it well anyway.

Don't document bad code - rewrite it.

Get the weirdnesses into the data where you can manipulate them easily, and the regularity into the code because regular code is a lot easier to work with

Each new user of a new system uncovers a new class of bugs.

90% of the functionality delivered now is better than 100% delivered never.

As we said in the preface to the first edition, C "wears well as one's experience with it grows." With a decade more experience, we still feel that way.