I am a F2P Runescape player and have had great success in raising my combat level by fighting Lesser Demons. Lesser demons are a level 82 monster that drop a multitude of items and can only hit an 8 on you. They are located in Karajama Volcano. I have spent hours a many down in that volcano, and have been very successful. If you want to be the most efficient and effective fighter down there, follow this very basic guide.
Note: You should be at least level 70+ to battle them to your full potential.
To set up for the lessers, gather full rune, around 500 lobsters, around 20k, basic teleport runes, a rune scimmy, a rune battleaxe, boots, gloves, a cape, and a power ammy. Equip all the armor and weapon and teleport yourself to Falador. Go to the Falador East bank and grab the 20k, 500 noted lobsters, teleport runes, and the other weapon (if you wish).
Next, bank as many lobsters as you have inventory space and then withdraw them as items. This should leave you with a full inventory. Now, run south to the Port Sarim boat and travel to Karajama. Run to the rope and go into the volcano.
Go around the peninsula to where the lesser demons are. If there are too many people to where you cannot snag one in a minute, log out and go to a world with around 1500-1900 people in it. (The more people there are, the less likely it will be busy down in the volcano and the quicker the lessers respawn.)
Once logged in to a world where there aren't many people, turn your attack to what you want to train, either attack, defense, or strength. The rune scimmy and battleaxe both hit well against them, so you should do just fine. Attack! When you get to around 40% of your hit points, eat a lobster (they tend to hit more when you are at, say 90%).
Repeat until you are out of lobsters. Pick up everything they drop, except ashes. If you are having a hard time getting lessers to fight because rangers or mages are snaking them, be on your toes and click on them right away. When out of lobsters, run out of the volcano and to the general store that you passed on the way in. Eat the banana that's sitting on the counter. Sell everything that you got that they dropped, but save chaos and fire runes to sell to players later.
Next, if there are cooked lobsters at the store already, buy them until you have a full inventory. If not, sell some of your noted ones then buy them back right away. Exit out of the shop window and eat lobsters until your hp is full. Buy some more lobbies until your inventory is full once again. Then, go back down there and fight! You should break even or make a profit each time, depending on your combat level. You might even get the occasional rune med every once in a while.
At any rate, this is a very safe and effective way to train. Some people are attracted to the greater demons in the deep wilderness because of their better loot, but don't be fooled. Those are rare and you're gonna get yourself PKed.
Happy Fighting!
