Some general programming methodologies

"MIT approach" with CLOS and Scheme:
1) Simplicity-the design must be simple, both in implementation and interface. It is more important for the interface to be simple than the implementation.
2) Correctness-the design must be correct in all observable aspects. Incorrectness is simply not allowed.
3) Consistency-the design must not be inconsistent. A design is allowed to be slightly less simple and less complete to avoid inconsistency. Consistency is as important as correctness.
4) Completeness-the design must cover as many important situations as is practical. All reasonably expected cases must be covered. Simplicity is not allowed to overly reduce completeness.

"Worse-is-better" philosophy is only slightly different:
1) Simplicity-the design must be simple, both in implementation and interface. It is more important for the implementation to be simple than the interface. Simplicity is the most important consideration in a design.
2) Correctness-the design must be correct in all observable aspects. It is slightly better to be simple than correct.
3) Consistency-the design must not be overly inconsistent. Consistency can be sacrificed for simplicity in some cases, but it is better to drop those parts of the design that deal with less common circumstances than to introduce either implementational complexity or inconsistency.
4) Completeness-the design must cover as many important situations as is practical. All reasonably expected cases should be covered. Completeness can be sacrificed in favor of any other quality. In fact, completeness must sacrificed whenever implementation simplicity is jeopardized. Consistency can be sacrificed to achieve completeness if simplicity is retained; especially worthless is consistency of interface.

Extreme Programming (XP) methodology:
1) Make samll, but freguent, release.
2) Develop in iteration cycles.
3) Do not put in anything that is not in the spec (no matter how tempted you are to put in functionarlity "for the future").
4) Writhe the test code FIRST.
5) No killer schedules; work regular hours.
6) Refactor (improve the code) whenever and wherever you notice the opportunity.
7) Do not release anything until it passes all the tests.
8) Set realistic schedules, based around small releases.
9) Keep it simple.
10) Program in pairs, and move people around so that everybody knows pretty much everything about the code.

Reference:
1) Wikipedia--Extreme Programming
2) The Rise of "Worse is Better"