5. Investigate the vendor
Once you've decided on a market and feel confident that you can use it safely, start searching for your drug of choice. Don't get ready to make your purchase as soon as you find someone selling what you're looking for. One of the greatest benefits of buying drugs online is being sure you're getting a quality product. Customers leave eBay-esque reviews for vendors, letting you know whether you're dealing with a legitimate salesperson or someone looking to rip you off.
(By the way, avoid anyone who requires you to pay them before the transaction is finalized. Most reliable markets require an escrow method of payment to make sure people aren't getting robbed.)
While no one should be buying hard, life-threatening drugs, those committed to doing so are a lot safer when they buy through darknet markets. They avoid the dangers of in-person interactions, can plan purchases in order to avoid buying too much at one time, and can investigate vendors to make sure they're not dealing with someone who delivers product laced with more dangerous substances.
Again, we must reiterate, no one should be buying drugs that can kill them. Get help. Right now.
That said, until we find a way to locate every addict and convince them to turn away from that behavior, being able to buy drugs in an environment that not only allows for safer usage, but actively encourages communication about quality and proper dosing methods. It's the best option for society as a whole.