1. Do wine of zammy or something to get up starter cash. Once you have about 100k or so go to a magic shop either Varrock or falador. Buy air and fire rune PACKS. Open them. Repeat until you’ve used all your money. Then take them to the grand exchange and sell. When you buy 1 rune pack you’re getting 100 runes for approx. 430 gp. Which comes out to 4.3 gp per rune. You can then sell those runes for 5-6 gp each. Netting you some very good profit without risking anything. You literally stand there and buy rune packs. No magic or weapons required.
2. Now only caveat to this is that you have to switch worlds. And you can’t switch worlds too quick or it’ll boot you. So buy up 1 full inventory of fire and then open them. Repeat with air. Then open. THEN switch worlds. That should give you enough time each world that it won’t kick you. It’s how I left f2p and I’ve not lost my membership.
3. DO YOUR QUESTS! I know it’s a sucky grind but they pay off in the long run and it’s easier to just get them out of the way rather than waste your 14 days on bond doing f2p stuff.
4. I left F2P high alching stuff. With about 100k I made a bond in about 2 weeks. Be sure to investigate a member moneymaker to support your membership.
5. Complete dragon slayer, buy anti fire shields from the NPC and sell them on the GE. You double whatever you put in at a minimum. So if you spend 100k, when you sell you'll have 200k minimum.
6. Buy OSRS gold bars and smelt gold rings. Stay persistent.
7. I made 50 mil in f2p over a year, all on mobile. I made most of it from flipping. I started with fishing for starter cash because of the nostalgia, but I dabbled in everything. I trained up combat and killed ogress warriors while leaving long flips in the GE. I spent time mining, superheating, smithing, and then high alching in fally mine. I got 70 crafting from emerald necklaces. Pretty much everything I did to build my account I did in a way that made me money instead of costing me money, and I flipped every day. I did a lot of fishing, mining, and combat for money, but I think woodcutting is probably the best (which I didn't do) because of the yews by the GE (if you can find a free world)
Hope it will help you, if you have better suggestions, welcome to your message.