Taronites

I have a little problem, because I get sometimes unwanted outlines with my layer 'objects' how can I fix it and how can I avoid this in the future? An example I will upload here ...

I imagine you are talking about the thickness of material on a layer. If it has any build-up, it will be lit, which will make the shadow of the lip around the spot appear like an outline. There are a number of ways to deal with it, but pretty much all of them will alter the way the layer looks, I'm afraid. ...but show me what you've got, of course!

thats my current project / WIP - not my personal planed DARK TOWER SERIES, but I have to do - 2 or 3 STORK ARTWORKS in the next days - but back to my question, how I fix/avoid the white Outline? You see that outline on the black sided wing of my stork and at the downside of the forrest.

Hmmmm....try selecting black as color and erase carefully around that edge. That might help!
Looking GREAT, though!