I have a 50mm prime lens that’s really awful at focusing. How do I learn to manually focus for street photography?
For street photography a good technique is zone focusing. For example F8 on a 35mm you can pre-set your focus to 8 ft which means that everything from about 5-1/2ft to 15ft away will be in focus. No waiting for your auto-focus to catch the subject, as long as they are withing the zone, it will be in focus.
Here is a site that explains this technique in better detail