Hi there, and welcome to the forums! If you're a new player, it can be a bit daunting to try and raise enough cash on a biweekly basis as you're competing with people who have a lot more experience and higher levels. So it might be better to use real money to purchase it, if that's affordable to you. In terms of in-game methods, some dailies like making vis wax in the runecrafting guild (requiring 50 Runecrafting) and buying supplies like many runes and broad arrowheads from Slayer masters, to resell them on to players via the Grand Exchange at a profit, can be fruitful. But again, these generally require you to have a healthy amount of start-up capital in order to use effectively.
"Fight for what you believe in, and believe in what you're fighting for." Can games be art?
My blog here if you want to check out my Times articles and other writings! I always appreciate comments/feedback.