I've always recommended studying what I call 'fringe crafts' or crafts that are similar to what you do, but are just outside the boundary so that they carry another name.
Examples are:
Saddlery
Bookbinding
Shoemaking
Upholstery
Leather architecture, sculpture and so on.
One of the best ways to learn is by watching someone who uses your material, but has a very different way of looking at it and working with it.
In the video below is Trevor Lloyd of Trevor Lloyd Ltd in Ludlow, England.
Here Trevor shows how he applies gold foil by hand to the goatskin binding leather he calls 'Morocco'.
To get to the ideal 100 degrees or just slightly under, he presses his stamps against a wet rag to wait for the sizzle to stop. So simple huh?
Note how this man's hands flow with intimate familiarity as he works on his books.
Pick at least one thing that you can take away from his video.
Perhaps the way he works in such an organised manner.
The way he has the text written out in front of him to avoid mistakes.
How he recommends polishing the stamps in order to leave a 'bright impression'.
The use of lighter fluid to remove excess gold leaf (works on foil too btw).
Learn to pick up on these little things and you will continuously grow!
Brilliant!