I am going to do some power leveling with my cheap runescape accounts.
There is a hole in the ground around where people are always mining. Right click it, Climb down Entrance will appear. It is the entrance to the Stronghold of Security. Goblins are perfect to kill the higher level. They are dead in about two to three hits and then you can be on to the next one.
If you are power leveling, you are most likely going to need food. At the end of each combat, there will be rewards for you. For just the first level, you get runescape gold! The prizes just go up from there. To save time, remember that farmer100 has awesome runescape accounts for sale.
Carry around some Tuna, and it might save your life.