Distance characters have a unique style of play that often forces you to build a deck specifically around them. This is because while distance characters are initially fairly ineffective, they can be a devastating force when paired with the right support cards.
Distance characters all have the special ability to attack from two spaces away. This ability also allows them to shoot across other characters to hit an enemy on the other side. However, distance characters also generally suffer from a very low defense.
Their initially low stats, and cripplingly low defense in particular, makes pairing them up with another ally a wise choice, at least for the beginning of the game. The ideal candidate is a hero or infantry card with a high defense. The major downside to using such a defender is that if both characters move that only leaves you actions enough for one attack.
You'll typically want to bury your distance characters at the back of your battle formation, to give them time to draw cards before bringing them into play. However, distance characters can also be good for aggressive plays, and have a far higher likelihood of drawing their needed cards if you focus your whole deck around distance characters. With two distance characters in your deck and doubles of all their needed upgrades, attack and defense cards you can afford to take a much more aggressive stance with your distance troops.
In the end, the key to using distance characters effectively is to realize their dependence on their access to support cards, and to do everything you can to strategically limit your dependence on the draw. Whether using them aggressively or defensively it is important to always keep in mind the number of attack, upgrade and defense cards you have coming and watch for opportunities to extend the distance character's advantage.