Step 1
Ask Wizard Mizgog for a quest.
Collect a red, black, yellow and white bead.
Give them to Wizard Mizgog.

Go to the third floor of the Wizards' tower, which can be found south of Draynor Village. Politely ask Wizard Mizgog for a quest (Picture). He will tell you that that Wizard Grayzag's imps have stolen four magical beads that he needs you to get back for him.

Now you need to collect some beads. You can either buy these from players - which may take a while - or you can try killing imps, which will still take a while to do. You will need to retrieve a red, black, yellow and white bead from the imps drops.

The image below shows two prime locations (south of Falador and around Karamja Volcano). Imps can also be found around Varrock and Lumbridge.

When you have retrieved them all from the imps, return to Wizard Mizgog and he will reward you.