To get started, make sure you realize what you're trying to pry: between the black back and the silver strip. This may seem obvious, but if you attempt to separate between the front and the silver, you could break the frame or spend hours fruitlessly. Better safe than sorry.
I used a real guitar pick (they're a little skinnier), and ran it along the edge with some pressure, on my phone the weakest point was around the corner, which gave just a hint of separation
Once you slightly separate it, you'll need something a bit more sturdy (the blue pick in this case, or even a spudger) to run between the two pieces