As @TaliciaDragonsong: said, no reason to get a guide. Game's super linear. Only issue you'll have is if you outlevel a planet (which you'll probably do if you do every quest there), in which case just do your class quests there until your class quests tell you to go to another planet, then go there. IIRC all the quests tell you the recommended level anyway. Just do quests around your level.