Fascinating article on a troubling paradox: approaches which promote transfer of learning on simple tasks (like varying practice), hinder learning of complex tasks. But fully-guided instruction on complex tasks hinders transfer.
This paper usefully articulates how transfer works: either through the abstraction of knowledge or the application of knowledge elements to new tasks.
And the paper offers some guidance on how to foster transfer (how complicated the problem is (element interactivity)) but do add germane cognitive load (vary practice, reduce guidance and feedback).
van Merriënboer, J., Kester, L. and Paas, F. (2006). Teaching complex rather than simple tasks: balancing intrinsic and germane load to enhance transfer of learning. Applied Cognitive Psychology, 20(3), pp.343-352.