EDIT: Sorry for no screenshots, check for the Death Plateau on a Runescape world map online if my instructions are too hard for you to follow.
In this guide I will teach you to get to trolls which give about 20k xp for every troll you kill to the combat stat you want to train. Beware as they hit hard for their level, at level 69.
1. Teleport to Falador.
2. Go out the North entrance.
3. Follow the path going towards the left until you come to a gate and enter it.
4. Continue along the path until you reach the Druids' Circle.
For lazy asses
, you can buy a ring of duelling which is player made. When you operate it, it can teleport you to the Heroes' Guild, skipping steps 1 to 4. You can buy one from a player I know. His username is No so add him if you want to buy a ring of duelling. But there is a catch. The ring of duelling costs 10k and has 8 charges, so use them wisely.
4.5 Move North all the way past the Heroes' Guild until you hit the Burthope Games Room.
5. Move east up the mountain path. This mountain is called the Death Plateau.
6. Congratulations! You have found the trolls! Now get training and don't forget to get food or pots where necessary.
The trolls, however, do not drop anything worth a fortune. They only drop grimy herbs and sometimes uncuts and of course, the coveted clue scroll which all monsters drop.
Advice:
For lower levels, you are advised not to train melee on the trolls as they hit hard for their level. You can train range or mage on them.
Also, strength pures should not train there because of their low defence levels.
For everyone else, wear some good armor, as I am at 81 defence and the trolls are hitting 7s on me, so bring cakes if you lack money, or buy lobsters from the pub in Falador and potions from Duradel in Oo'glog if you can to maximise the amount of xp you get from fighting the trolls.