The Way and The Rules
Ommmmmm. We can learn so much from the Monks of History, can't we? As for instance:

The Way of Mrs Cosmopilite
Everyone knows that living your life by the mystic sayings of ancient, bald monks living on mountaintops works wonders for city dwellers, right? So, where do the monks go for their distant, incomprehensible wisdom? Ankh-Morpork, of course!

Behold Lu-Tze's path to enlightenment: The Way of Mrs Cosmopilite, 3 Quirm Street, Ankh-Morpork, Rooms for Rent, Very Reasonable.

The Rules
I have also included the only four examples of The Rules that have thus far been revealed to us.

The page numbers are mainly for my benefit and refer to the Doubleday hardback versions of the books.

The Way of Mrs Cosmopilite
Oo, you are so sharp you'll cut yourself one of these days.
(tot p44)

I'd forget my own head if it wasn't nailed on.
(tot p51)

There's a lot goes on we don't know about, in my opinion.
(tot p57)

There is a Time and a Place for Everything.
(tot p71, p96)

I have only one pair of hands.
(tot p72)

It never rains but it pours.
(tot p72)

I can't be having with that kind of thing.
(tot p72)

Hard work never did anybody any harm.
(tot p92)

It does you good to get out in the fresh air.
(tot p92)

Because.
(tot p92)

It won't get better if you pick at it.
(tot p93, p122)

Eat it up, it'll make your hair curly.
(tot p93)

Everything comes to he who waits.
(tot p93)

I haven't got all day, you know.
(tot p94)

I was not born yesterday.
(tot p95)

There is no time like the present.
(tot p97, p306, p312)

You can't tell a book by its cover.
(tot p98)

You've got to learn to walk before you can run.
(tot p101)

Well, I'll go to the foot of our stairs.
(tot p108)

You could knock me down with a feather.
(tot p114)

I've got a feeling in my water.
(tot p116)

I'm not as green as I'm cabbage-looking.
(tot p116)

Big events always cast their shadows.
(tot p139)

We live and learn.
(tot p152)

A washed pot never boils.
(As said by the yeti. It should probably be: A watched pot never boils.)
(tot p160)

If you want a thing done properly you've got to do it yourself.
(tot p161)

Seeing is believing.
(tot p161)

Koan 97: Do unto otters as you would have them do unto you.
(It works in its current form, but is probably a corruption of: Do unto others as you would have them do unto you.
(tot p255)

Koan 124: It's amazing what you see if you keep your eyes open.
(tot p256)

When you have got to go, you have got to go.
(tot p275)

You should always wear clean underwear because you never know if you will be knocked down by a cart.
(tot p275)

If you have another one you won't have an appetite for your dinner.
(tot p277)

You never know what's going to turn up.
(tot p297)

A penny saved is a penny earned.
(nw p81-2)

The big sea does not care which way the little fishes swim.
(nw p217)

The Rules
Rule One
Do not act incautiously when confronting little bald wrinkly smiling men.
(tot p50)

Rule Two
Never refuse a weapon.
(tot p99)

Rule Three
Be frightened when holding a deadly weapon and facing an unarmed man in a pose of submission.
(tot p100)

Rule Nineteen
Remember Never to Forget Rule One.
(tot p308)