There's plenty of autoer's on the forums that feed your character when it's health gets low...but from personal exp. and buying alot of sets of rune armor you are better off fighting mobs (monsters) that you can kill fairly quickly and do little damage.
Level 3-35
Train at the chickens either south of falador or in lumbridge (North east and north west)
Why chickens? Chickens die quick and if you have an autoer to pick up feathers you can sell the feathers for supplies. If you looking for which color to select for declare monster form I suggest picking the red (whatcha ma call it) on top of the chickens head, and then one color of the chickens body. Some chickens have multiple colors so select one of each. (eg. brown of brown chicken, and tan of tan chicken.
Level 35-60 (str:40-60)
I discovered a great place while looking for a place to train my pure str. character which was was mid point between weak and strong (level 36). Directly north of barbarian village and south of edgeville there is a training safety school. Go through the back of the school and talk to the guard, read all the plaques, go upstairs do talk to the teacher and do the test. Trust me its worth it. Pass the test (really easy) and you'll get to exp lamps woot! and a lame emote. Go back downstairs, look at the empty cell with the poster and pull that shit off! Tada you are now in an enclosed place with mobs perfect for 35-60. Great thing is no one comes down there often, and the monsters are confined. 35-45 i'd fight muggers, 45-60 fight the spiders. Theres more of the cave, but i haven't explored all the way....I just set up my autoer and went to work
Level 60+
Hands down the best place to train is in barbarian village strong hold of security. Its directly in the middle of the village. If you are training range and have 60+ range i suggest training on minotaurs as they drop iron arrows often, you virtually never run out of arrows. The place is swarmed with monsters from low level and high level. I'd stick with goblins and minotaurs till 95+ then move down to the zombies and what not.
Well those are some good place happy autoing.
I recommend Narcles Fast fighter its the shit!!