So what you do, first, you must get your magic up to level 9. You can do this with the Witch's Potion, Imp Catcher or RuneScape gold even at the Dummies. Secondly, get a fire staff and Mind and Air runes. You'll need twice the amount of Air Runes as Mind Runes and If you've got 5k minds, you will require 10k airs.
Thirdly, just head to the spot where you can train and take on a Mage Dummy. Servers can only have three people at once, so there are very few people. The only thing you need to do is click your mouse and move the camera every 5 minutes. But it's not allowed. It's not possible for beginners to "die" because they recuperate their full health after every attack. This is a brief video of my personal character training here.
I've had many discussions (arguments) regarding this issue recently with CC. Most people like "slayer dart" for barrows. Even those at the top levels of lvl are convinced that slayer dart is the most effective barrowing technique. It could be more suitable for you, depending on your playing style. High mage (85+), 90+ def and 80+ prayer could also be available. Which means you can do 342147219 chests a trip. Good for you, but melee is better for me. I make more money by not wasting money on 100+ slayer dart casts and I am able to cheap OSRS gold do more chests per journey.