I feel you! I didn't use to have issues with writers block before doing reports and school assignments, mostly because I got pretty good at just throwing stream of consciousness at the page and it ended up being good enough.
With my fiction writing now, I feel a lot more pressure to make it as polished as possible and do the concepts and themes I want to write justice, so I get caught in a trap of second guessing and getting stuck over trying to make something perfect.
I've been able to combat with a couple habits. Whenever I get stuck I put on music that I like or that fits the mood of the scene I'm trying to write, and even if I'm feeling uninspired I'll force myself to put down whatever comes to mind with the intention that I'll either edit or delete it later, so it doesn't matter if its good or not.
In extreme cases this still wont work for me. Like in my main story I'm writing now there's a big chunk of important exposition in chapter 5 that I've already written but hate, and whenever I try to go back and edit it I just can't think of anything to make it not suck. So instead of just staring at that bit I move to scenes immediately after and work on those until my creative juices become unclogged.
But yeah, thats the gist of my strategy. I've also heard it helps to have a dedicated Writing Station (TM) that you only use when you're writing and that allegedly helps get in the mindset, but I just write on my couch and wherever I am when an idea pops into my head.