By now I presume you have 41 mining. You have the ability to mine coal and gold. If you can scrape together 20k, I highly recommend you buy a rune pickaxe from the Grand Exchange. As far as mining goes, it would now be wise to switch from iron to coal. At this level you will have to make do with the coal rocks in the Barbarian Mine, but it will be worth it soon enough.
If you still have some iron left in your bank, one possibility is to begin smelting steel bars and selling them for money. One steel bar requires an iron and two coal, sells on average at 600gp each. However, if you do not have any iron left and do not feel like getting more, or you do not have 30 Smithing to smelt the steel bars, you could also just mine coal and sell it for about 200gp each. I must admit, this is where mining gets the most boring thus far, so make sure you keep at it.
You could also continue powermining iron if you wish; the best place is in the Grand Tree mine, as there are about 6 iron rocks right beside each other. Simply mine one ore, drop it, then move on to the next one - this is very fast exp. A great way to end up with a small profit and fast experience, is to mine in the Dorgeshuun mines as there are many rocks and Mistag the cave goblin will buy all your iron ore for 13gp each. If you have access to the Culiomancer’s chest, then banking the ore wouldn’t make much trouble.
Another alternative for members, is that of mining granite at the desert quarry, located south-east of the Bandit Camp. The experience for these ores is greater than coal, and can be mined with great ease.
The mine south to Falador, has many rocks, including iron and gold. It’s a good spot to powermine iron ore and bank isn’t that far as well.
Finally, members can also try the Coal Trucks. North-west of Seers’ Village, there are 17 coal rocks (which are usually fairly empty) just south of a number of crates. Once you’ve filled up an inventory of coal, put your ores in a truck, and go back to mining! The trucks hold 120 ores, which is just over 4 inventories. Once the trucks are full, or you’re done mining, you pick up the coal in Seers’ Village - just north of the bar - and deposit all the ores in your bank. It is recommended to have 20 agility when you’re using the Coal Trucks, as it cuts the route back to Seers’ considerably. Be aware that random events tend to occur more than usual here.