Put muddy keys in the Lava Maze. Only take the most valuable items. This is the best way to earn cash from f2p. I can make RS gold 400k/hr with this method if I'm good. However, the muddy keys cost a lot and take time to buy. Utilize a gem bag to get maximum efficiency. Mine adamant ore. I like to do this in the hobgoblin mine, wear the full batwing and shield, and you'll not need food. Hop worlds. You don't even need to think about it because PKers are rare in this region. If you'd like to prolong your travels, you could superheat coal mines. But, I'm not sure if this is more efficient. Superheating is 70 miners, 70smithing
Use rune arrows to defeat more demons at the Forinthry Dungeon. 100k gp/hr is the highest level xp that I have seen for players who are free. Air runes average around 200k/hr at the 66 runecraft. The more you can earn is, the better. However I haven't tried it in a while. Ideally, you should just purchase a bond and earn money by using one of the members methods in the event that you only play for every day for an hour and have good statistics.
Comment/tweak or even add things.
While I am not an expert on how members make income, there are some things you can do at no cost. Kill Hill Giants are found in the Edgeville's resource liard. Grab the bones and the limpwurt root. ~250k gp/hr last Summer. Take through the mud of keys towards the Lava Maze and only take the most valuable items (you shouldn't consume anchovy pizzas). This is the most effective method to earn f2p. I'm estimating 400k/hr however it takes time to collect muddy keys.
Mine adamant ore. This is what I do. It's not even necessary to have food if you're wearing full shield and batwing. Hop worlds. The PKers here are so rare you don't even have to think about it. If you want to prolong your travels and you want to extend your trip, you can superheat coal mines. However, I am not sure if this will be more effective. 70 miners, 70smithing required for superheating. 200-300k gp/hr.
Use rune arrows to defeat other demons in the Forinthry Dungeon. 100k gp/hr, plus it is best range xp for freeplayers that I'm aware of. Multicombat is a great option to save time and not wait until you kill the next demon. I think doing air runes is around 200k/hr on buy OSRS gold 66 runecraft The more powerful the better. I haven't done that recently though.