DO - commission a suit of spiked plate mail.
DON'T - forget to say 'on the outside'.
DO - wear your spiked armour into battle.
DON'T - wear your spiked armour into the crowded tavern.
DO - leap into combat with a blood-curdling cry.
DON'T - leap into combat over the head of another PC, causing both PCs to collapse to the ground in an unsightly tangle when you realise you can't jump that high, blocking the approach to the enemy for everyone else in the party and allowing him to get away with his nefarious deeds.
Guess which one I DMed?