Ranger is a class mainly specialized on ranged combat (Sharpshot, Doubleshot) and stealth (Camouflage, Conceal) giving them various advantages of Mages, Druids, and Rogues.
Since Rangers are better from a distance than in melee range, use Bolas to slow an enemy, and while the enemy slowly walks towards you, continuously attack it, retreating when they get close. This tactic gives a big advantage, since by the point your opponent gets to you, he/she is already greatly damaged. It's recommended that after casting Bolas you use Rapid Shot. There is no specific strategy in fighting with enemies that attack from a distance. While Rangers can use spears, it is recommended to use a bow.
Rapid ShotDouble Shot