As a ranger,we cant carry anything in our other hand to gain energy since the bows are two handed, so we rely in armor some armor and bows will give more energy. In post you can have a crafter build you armor that will give you a enery boost. Timing is everything in ranger skills....I am a ranger/mes and it took me awhile to figure out how to time skills so I am not always out of energy...
I think Lions arch is the first place you can get Druid armor and The can buy the bow string for anywhere from 250g to 1500g ask around. Other option is use the monk staff and an energy item