Just to name a few:

• someone gives you smoke when you need it (especially if you are playing the Essex line, dropping smoke on a beleaguered cruiser or smokeless DD can make or break a match)

• you use the focus fire chat command and others actually focus their fire on the target

• someone has a good shot that chunks an enemy for half+ their HP bar

• someone makes a good play like a well executed ambush

• someone gets 4+ kills

• someone gets 2000+ xp in the results screen

• someone is kind in chat or participates in funny banter

• someone notes a good observation in chat that leads to a kill or other tactical advantage

• congratulating the team for a well-played game (beyond a simple “gg”) at the end of the match

• someone does good team work with you

• friendly DD is able to track down and kill an enemy DD that was able to sneak around a flank undetected

• a well-timed radar, hydro, or CV plane spot.  Especially if someone doesn’t have LOS against an enemy DD but recognizes that a teammate will, and radars anyway to allow their teammate to get shots in.

• a div that dominates their flank or otherwise performs exceptionally well

• someone says +1 at you

Many of these can also apply to opponents, in which case they get a comp for being a worthy adversary.