plastic won't stay put!

[corim123]

If the bed isn't level, you're asking for trouble regardless of the tape or goop you use to help it stick.

Normally, I'd say that if you can't level your bed to +/- .001" (one mil, or about 13 microns), lay down a raft first.

Since you are using 300 micron layers, when you slice, just set the first layer height to 250 microns - this will cause a little overfill, and the material will be forced more firmly onto the build surface. This should be enough to overcome a small variance in the build surface.

This is excellent advice. I also suggest using a piece of paper to judge how close your nozzle is to the board. Getting that homed in and using this above tip will overcome some slight leveling issues and allow you to get adhesion. That and blue painters tape.