Some good places to look for drug dealers include:
Parks
Bus stops
Alleys
Sidewalks near bus stops, parks, and alleys
You'll get calls about reported drug deals.
When at any of these places, look for two people talking to each other. If one of them hands a brown bag to another person, that means a deal took place. You can even use intuition (LMB by default) to focus on the deal. Be careful when using your flashlight at night and keep a good distance away from the deal.

After you spotted the deal taking place, run up to the dealer and detain them for distributing drugs. After detaining them, an intuition message usually comes up about them being anxious or nervous. Since you witnessing the drug deal is probable cause, you can search the dealer right away.
If done correctly, you should find bags of white powder on their person. Finally, arrest the dealer for distributing drugs (under the narcotics section) and call transport. If the dealer flees when you attempt to detain them, bring out your taser and make them stop.

After arresting the dealer, you then go up to the drug buyer. You detain the buyer for possessing drugs. Like the dealer, an intuition message about anxiousness usually comes up. Then, you do a full search of their person. If done correctly, the buyer should have bags of white powder on them as well. You then arrest them for possessing narcotics under the narcotics section.