Players who use CC well or use it at all should be nurtured. Players who break CC before time should be mercilessly mauled.

Interrupts are also important, but I often find it harder to work out who provided them (any tips?).

A tank who has the guts to do a big pull is something to treasure. Anyone who pulls before the tank needs to go to the naughty corner.

Cheerful and chatty people are also worth a lot, and good teachers are absolute gold.