So the streets is a different world compared to online. I'd recommend a good quality product. Clubs are a good place to find buyers. You have to find the demographic of people that use the drug you sell, and go to places those people frequent. You have to feel it out. But your game is going to be word of mouth. Get your product to people who hopefully have friends that use. Remember to tread with caution. An undercover or informant would suck to sell to. But this might not be a top worry until you get bigger
Police are undercover in bars and nightclubs often. I wouldn't try to sell anything to anyone I didn't know there. Music shows, festivals, the ghetto. Depends on what you are selling. I couldn't sell any heroin at the bar and I couldn't sell any cocaine in front of the homeless shelter.
Online clients are different. Your goal there is to get your product in front of as many eyes as possible. I would set up vendor shops in several of the major markets. Make sure you give a great product and excellent customer service to your first buyers (you should actually continue this but it is very important in the beginning). Maybe even though in some freebies. When you have somes sales and good reviews, new customers will come. Free samples for a review on a forum is also good