Use the keys that are muddy through the Lava Maze. Take only the important stuff. This is the best method to earn f2p. I'm estimating 400k/hr but it takes a while to collect dirty keys. Gem bags are the most efficient choice for the RS gold highest efficiency. Mine adamant ore. I like to mine this at the hobgoblin mining location. Wear full batwing, shield and food isn't necessary. Hop worlds. It's not common to see PKers in the area. Superheating can also be done through mining coal. This will prolong your travel time however I'm not convinced that it's more efficient. 70 mining is required, 70 smithing if superheating.
Use rune arrows to defeat more demons at the Forinthry Dungeon. This is the most powerful range of in xp for free players and offers 100k gp/hour. Air runes average about 200k/hr on the 66 runecraft. The more you can earn is, the more favorable. But, I haven't done OSRS buy gold this in a long time. It is recommended to purchase a bond, earn money using one of the members methods and only play for one hour per day, as long as you have good stats.