Of course, pvming like slayer, bossing, and zulrah are great for money making.
If those aren't an option because of stats, you could always passively flip in the GE while you train. I've found this to be a great method because you can play the game while not worrying too much about money. Another idea is making (3) pots or (4) pots by buying pots in the GE and using the decanter. Last but not least, runecrafting.
If you do the last one legit for too long you'll end up getting cancer.