Count On Your Partner -
As a rule of thumb, you should count on your partner to take one trick. That means, if you're deciding to make trump or not and you're sure you can win two tricks out of the minimal three, go ahead and call trump. Chances are, unless your partner has a really crummy hand, that he or she can win the third trick and you’ve gained a point!
Source of text: http://voices.yahoo.com/tips-play-euchre-like-pro-16270.html?cat=7