Requoting this because it's fantastic advice. There's plenty of courses that teach you this, Krenz Class 0 being one example. Work your way down from larger shapes down to smaller shapes and compare against the original once or twice. It's slow at first but you'll get faster with practice.
The Tired Dev - Art Training: The Sequel
When I say you don't need to trace I don't mean "you need to get good" I mean you can use tools besides tracing to help you utilize your references. One example is using a grid, where you can zoom into one tricky area of a complicated ref and break it down by section
