Other than what others have suggested:

• Do get an etch resist pen. The toner occasionally, even when it goes well, might not transfer on some spots of the copper plate. So you’ll need the etch resist marker to color in breaks in paths etc. and fix these little issues.
• The acid or whatever you use to etch away the copper might not work on some spots. Leading to shorts or otherwise unwanted connections. So do check with a multimeter the paths and pads that are close to make sure there arent shorts.

I dont think theres much more to add, its quite a simple process. Have fun :)