In my opinion this is a bit like asking which came first, the chicken or the egg.
Personally I think that the two must go hand in hand. It is a good idea to study the basics of magic so that you understand how and why it works and what is necessary in order to successfully cast spells.
But at the same time that you are studying you need to be practicing those same basics such as visualization, focus, energy manipulation, etc.
You can't cast a successful spell without having mastered the basics, and you can't begin to learn the basics without understanding what magic is and how it works.