The rules don't mention this, but can team mates discuss how/what they're going to play during a round? And can they reveal what cards they have to each other? I can't recall seeing anything about the hands of cards being secret from each other [you'd obviously never reveal your hand to your opponent team members, but YOUR team members, seems like a strategically viable thing to do].
I would never allow hands to be revealed to partners. Then you might as well just play with less people and more cards in your hand.
Normally, we play 'no table talk', meaning you can't say ANYTHING that could hint to your partner what you have or what you can do. Like Darin says, you need to infer what your partner is going to do based on how they are playing (what cards are played, passed, if they lay trump to take tricks away, etc.).
What Andrew does with giving hints is a no no in our games but truly, there is no right or wrong, it's just how your group decides to play the game. The beauty about trick taking games is there are so many ways to house rule stuff and all of them lead to fun times.