Tevo Tarantula, how to make it better?

[Dirk3D]

Hi! This is my first post here and I hope I will find a lot of information / ideas for my 3D print hobby...I have a TEVO TARANTULA 3D printer. i build it myself and for me the results so fare are OK-isch...It seems I have some recurring issues whenever I print.Measures I took: Leveling the bed as precise as possible with the paper method.Tightening the belts by printing a belt tighter.To me the axes look stable enough...I did not try different settings yet like temperature / speed / extruder settings...Would any of you have ant idea what the problem could be? * The angle of the print is not 90° but more and leaning to the backside of the print * The first layer is not as nice as the top layer and stopped sticking to the bed like it did before. (even some wrapping now and then) * It seems there is a bad layer in all my prints at like 0.5cm height...I added some pictures to make it more clear.Help and suggestions are much appreciated!RegardsDirk