Pocket square “rules” applicable to me; you do whatever you like:

1.  Always wear one; two if overcoat has a breast pocket.  Exception for heavy odd jackets and overcoats if gloves stuffed into breast pocket fingers up; but if most of time is to be spent outdoors wearing the gloves, then must wear square.

2.  White linen or cotton rarely; more frequently with black tie (especially if wearing colored boutonniere or socks) and town suits for weddings, funerals, religious observances, very serious business and court occasions.

3.  Solid color silks/linens/cottons second in rarity only to white linen/cotton.

4.  Square must contrast in tone with tie; no dark tie/dark square, light tie/light square, or bright tie/bright square combos.

5.  Colors/patterns pleasing with but not matched to or overly coordinated with colors/patterns of tie, shirt, suit/jacket.  Actual discordance can work.  Closeness or matching in principal color(s) of square and socks permissible.  Cannot define “pleasing”; just know it when I see it.

6.  No TV fold or precisely arranged points.  Stuff it puffed, points up/flopping, or both.

7.  See one I like, buy it.  Figure out what to wear it with later (sometimes years).

8.  Corollary rule: no one-for-show, one-for-blow.  This one pains me due to lack of elegance; but carry a pocket pack of tissues for blowing/tearing/mopping.  In the event a tourniquet is needed, sacrifice square (try not to get blood on rest of clothing, and replace square as soon a practicable).

9.  Placeholder for more rules; just thought about it in any organized way for the first time.

10.  Get a life.

Ah, tie length rule:  Wherever the tip ends up (down), it must not be visible between the quarters of one’s buttoned jacket.  For that matter, neither must one’s belt/waistband.   I insist that my tie tip just overlap the top of my waistband.  All of this means that the tip of my tie, and the waist of my trousers is covered by the buttoning point of my jacket.  This rule business is a quagmire.

An old one:

Suit, shirt, tie.

Only two items to be patterned, the other to be plain. Pick your own combinations.

Three patterned items is for the experts only.

Bacause I say so!

te.

(I suppose that the opposite 'rule' is fine too - Only two plain items, the other to be patterned).

I think I remember you in my class!