Now that you are Mithril equipped, you can start fighting some tougher opponents, ones that will get you more experience. Unfortunately, the days of fighting enemies that will give you good and free food are over, unless you want to keep fighting cows and chickens. You can do this, of course, it will just take you longer to up. It is always a trade-off. To level up fast you will need money to buy equipment and food. You can sacrifice the time by fighting weaker opponents that won't even require you to eat because you kill them so fast they almost never hit you, or you can sacrifice time by opting not to make money on the better equipment that will let you level-up faster. When you start needing food to keep fighting, you can take the time to build up your fishing and cooking levels instead of buying food, but this also takes time. It's all up to you.
Once you have Mithril equipment in runescape accounts, you can start focusing on fighting creatures that are a little tougher, ones that do not drop food, and ones that can drop items like weapons, armor, and gp's. You have lots of opponents to choosefrom in these levels, but you will need to start buying food because you will die without it.

next: Growing Stronger in runescape 2(Levels 20-40)