When I make a new frame, I have to try and copy all the layers to the next frame. Sometimes when I do this, not all the layers are copied and in some cases, only a part of the layer is copied. If someone could help me with this, that would be great.
What do you mean when you "make a new frame"? Just extending the timeline by a frame (F5) will automatically bring everything forward into the new frame.
You can select frames across all the layers you intend to extend, and then use these shortcuts as described:
F5: extend the frames without creating a new Keyframe
F6: Create a new Keyframe having all the previously drawn content as well.
F7: Insert a new 'blank' keyframe.