GETTING A TASK:
Talk to duradel, and he will give you a slayer task. many of the monsters will be in the slayer tower, except for hellhounds, dragons, and demons. A good tactic for making money off of slayer is to use ::taskreset to only get those two monsters *green dragons mainly* upto 80 slayer. You can also use ::taskreset if you have trouble finding the monsters.
NOTABLE MONSTERS/LEVELS TO REACH:
both green dragons and lesser demons can be gotten as a task from level 1. Monsters that do drop good items are:
Nechryaels - drop dragon boots. these can be killed at level 80 slayer.
Abyssal demons - drop abyssal whips. these can be killed at level 86 slayer.
Dark beasts - drop dark bows and dragon arrows. these can be killed at level 90 slayer.
Black dragons - drop some dragon items and draconic vissages. these can be killed at level 1 slayer I'm pretty sure. correct me if i'm wrong.
----be patient with these monsters, drop rates are low, but some days are better than others---
MAKING MONEY:
by 99 slayer, you should have alot of pxp from tasks, and depending on how lucky you are, you have plenty of drops to sell for alot of cash. dont forget to get that cape to show off to your friends!
(nechryaels, dark beasts, and abyssal demons are all located on the 3rd floor of slayer tower)
Hope this helped, please give me feedback, i hope to do more guides in the future with pictures to help out. :awesome