When you first start to train your range, you should start by the cow farm in Lumbridge or train on barberians at the Barberian Village. When your range level is about 20, you can train on minotaurs in the first level of the barberian stronghold. When you reach 30 range, you should use a maple bow and train on the zombies or flesh crawlers on the second level of the stronghold. When you have 40 to 50 range, you should complete the dragon salyer quest. Go to Crandor island and train on the moss giants, attack from between the mining rocks so they cannot attack you. When you have 50 to 60 range, you should train on the lesser demon behind the cage at the wizzards tower.
It cannot attack you so do not worry. If your mage level is atleast 40, you can use the spell called telekenetic grab to retrieve your arrows. When you have 70 range or higher, you can attack the ankous at the last level of the stronghold or you can go to Crandor and fight the lesser demons there. You can also go and train on the cockroach soldiers at the safety stronghold. You should use the best equipment and arrows that you have to level up faster. If you want, it would be easier to become a member and get your agility level to 50. If you have 70 range, you should use a crystal bow as it does not take any ammo. As a member, you get more equipment to use so it would be easier to train your range because you would be hitting better.
Members also have many more places to train. Other places that are also good for training: When you are still a beginner, you can train on the goblins by Lumbridge. Please tell me if this was helpful or not, you can also write any other places that are good for training range. You do not have to follow this, it is just to help if anybody needs it.