Legal Communication in euchre, page 1
Correct method of communicating with your partner
Communicating to your partner what suit to lead back is an essential skill in euchre. Good players don't just randomly select the cards they play, but instead read their partner's signals. Not hand signals, but messages sent by the choice of card played. Armed with this information the partner can lead back the correct card or suit. You can give your partner a lot of information simply by the way you play your hand. All the top euchre players work as a team, with each member watching for the visual card clues given by their partner. Let's see how this works in practice.
One classic situation is leading the right bower and finding your partner void in trump, but they hold an off-suit ace-king combination. By playing the ace on your lead, they are signaling that they hold the king of that suit. You now know that leading that suit back would be the best way to bypass the opposition and give the lead to your partner. Of course, this also tells the opposition what not to lead, but it will help your team more than it will hurt it. Keep in mind that this works not only on at trump lead, but on any lead where your partner cannot follow suit.
Often your partner won't have an ace-king combination, but instead will have an ace along with a lower card of the same suit. In these cases your partner would play the lower card indicating they have the ace. While this is not as straightforward or definitive as showing an ace, it's a good indicator and better than nothing. (Note that if they are throwing off a singleton and voiding themselves in the suit, it is still a good suit to lead back for your partner to trump in).
-> It is important to note here that the rules change if your partner is the dealer. Why? Because the dealer has had the opportunity to short-suit their hand, creating a void. Therefore, when they throw off, they are likely throwing from a suit in which they hold two cards. Say hearts is trump. You lead the ace of diamonds and your partner (as dealer) throws off a club. The best way to get back to them is play a spade, not a club! They most likely will be void in spades, so leading that suit will give them an opportunity to trump in and take the trick.
Look at this example:
Stay tuned, I'm looking for a better example
Suggested Further Reading: