When I'm looking at the screen, and nothing's coming to me right away, I start to get a little frightened. This should be easy. Write one word and follow it with another, etc. When I'm writing I usually get assaulted with words. Like some unseen word fairy chuckin' words from the aether to the front of my brain which translates to my fingers typing it out.
When the front of my brain isn't being pelted, that's when I start to think I have to "try" being a writer and that's what unnerves me. Words manifesting from nowhere feels natural and therefore propels me into believing I'm a writer. (The way it's supposed to be.)
It gets bad when I've been thinking about what's supposed to come next for too long. (Not from an plot outline standpoint, but what's happening in the scene.) Thinking and thinking ends up working against me. I start thinking about the laundry, what I'm going to make for dinner tonight, food... food... lunch... is it lunch time yet? 9:20 a.m.? Shit! I'm kinda hungry now. (So I get up for a snack.)
(Comes back from the snack) What now? Oh, writing! Where was I?
After I take a minute to reinsert myself into the Matrix, I usually end up throwing up words on the screen just to prove to myself that they don't belong there. Like when a quarterback is forced to leave the protection of his defensive line or be sacked. It feels like I'm "out of pocket" when I'm trying too hard, and I'm forced to make rash decisions to move forward.
But, sometimes when a quaterback is forced out of pocket that's when sight lines become clear. It's never a waste of time to try something that may or may not belong. If only to prove that it doesn't belong there. Moving away from what's expected can sometimes lead you in a more interesting direction, or show you're not going in the right direction and need try something else. Keep tinkering. Eventually the word fairy will chuck the right words at your brain.