The excellent Twelve Virtues of Rationality by the even-more-excellent Eliezer Yudkowsky, simplified to fit into the Common Meter.

The first is Curiosity:
to hunger for the chance
to solve, not worship, mystery,
to go past ignorance.

The second is Relinquishment:
to let the truth destroy
all false beliefs and not lament
them if they gave you joy.

The third is Lightness: give up all
attacked by evidence.
When thoughts are wrong, just let them fall,
let evidence advance.

The fourth is Evenness: Don’t take
a side against or for
beliefs. You are the judge, you make
your judgement by the law.

The fifth is Argument: to see
if friends will disagree.
With them, you practise honesty
before reality.

Empiricism, number six:
observe, try making sense,
look what your sense-making predicts
about experience.

The seventh is Simplicity:
much detail is a trap,
each part can bring catastrophe.
Take care at every step.

The eighth one is Humility:
prepare for your mistakes.
We’re learning rationality
through errors that this takes.

Perfectionism, number nine:
Find errors to remove.
It’s not enough to just be fine,
you always must improve.

The tenth one is Precision: speak
as carefullly as you
can dance towards the truth you seek.
Cut deeply at what’s true.

Eleventh then is Scholarship:
Learn math and science and
whatever else you need. Equip
yourself to understand.

Before these, one without a name,
though sometimes called the Void…
by any means, cut to one aim:
to leave mistakes destroyed.