Slayer is a skill that reqires you to kill monsters and here are the guides for where the monsters are File:Slayer.jpg
To get a task (which lets u get slayer experience) talk to Vannaka in Edgeville dungeon.
White Knight Can be found at falador castle.
Kalphites (Soldier, Guardian, worker) Can be found near falador east bank. Jump in the hole to get to them.
Green Dragons These can be found north of edgeville. Her is a map that shows the location Map. I suggest to range Green Dragons. If you are bit higher combat you can melee them but be aware always equip antidragon shield.
Battle Mages These are found in the mage arena. The mage arena is close to make bank. Battle mages hit hard with mage so mage protect comes in handy. I suggest equipping max 3 items to kill these because its wildy and you will lose everything if killed.
Giant Bats. Can be found next to the mage bank. They are low level and easy to kill but I suggest equipping only 3 items because you can get player killed.
Daggonath prime, rex and supreme They all can be found in the dagg lair. I suggest a godsword to kill these. Prime: Protect mage Supreme: Protect range Rex: Protect range If you have low prayer level I suggest taking some prayerpots because this guys have lots of hp and are sometimes hard to hit.
tzhaar-xil; tzhaar-mej; tzhaar-ket; They can be found near fight pits. I suggest for the lower levels to pray melee against them the higher levels can just kill them without.
Chaos Druids / Gargoyles These are found in the cave.