Unfortunately, copying layers from one Photoshop document to another isn’t quite as straightforward as copy and paste.
However, it can be done very easily, in a way that not only allows you to copy the layers but also position them consistently on the canvas.
How it's done
With the layers you want to copy selected, hold Shift and drag them to the tab of the document you would like to copy them to.
After a second of hovering over the tab, you’ll automatically switch between documents.
Drop the layers anywhere within the window (not on the tab itself) and they will appear on the canvas, perfectly positioned.
If you simply want to make a fresh start, you can copy layers to a brand new document.
To do this, select the layers you would like to copy, then go to the Layers panel (Window > Layers).
Right click and choose Duplicate Layer (or Duplicate Group, whichever option is available).
This will open the Duplicate Layer dialog box, which gives you the ability to choose which document you would like to copy the layers to. Select 'New' from the drop-down menu and click OK.
This will create a new document using the same settings as the current one, but containing only the layers you've selected.