That blank first page or empty black screen is the scariest part of any creative project.
What Mara mentioned about rewrites is key. Just understanding that you'll probably erase it all anyway is a great way to remove the tension from those first steps, make them feel less pressured, less critical. I start writing as best I can, knowing it probably won't be perfect, and make some headway. after I've jotted down a good bit, I take a step back, narrow my eyes and gaze at it all suspiciously, wondering if I'm making a terrible mistake. Then I throw away everything I don't like, and start over again, but this time there are a few edge pieces of the puzzle already in place, helping to define the shape, and it's easier that time. Through this whole process your subconscious mind is kind of grinding away at all the thoughts you've gone through, and a few versions later it all tends to start coming together into something coherent.
Indie hit on something important, which is to strategize your work from a top down perspective. Working backwards can produce complex resolutions to plots that will make you appear brilliant to your reader. You might consider starting from a template for your early works, just to build confidence and experience. Like a sitcom episode is an example of a template, or a Law and Order episode. 2 detectives, 2 prosecuters, one criminal, etc. It can give you a starting point to alleviate some of the fog and get you moving.