"Should a professional player learn by heart how to refute dubious opening schemes? The Greco Counter-Gambit, the Albin Counter-Gambit, the Schara-Hennig Gambit, the Canal Variation... In principle, learning by heart is not harmful - any exercise develops the capability of the organ being trained, in this case the brain. But, one might ask, what for? I saw the young (then) grandmaster Smyslov, on first encountering the Schara-Hennig Gambit, attempt and succeed in refuting it 'at sight', as musicians would say. We remember the famous game where Marshall first employed his attack, which had been worked out in detail at home - against Capablanca, and the latter refuted it at the board! Obviously not everyone can be a Capablanca. But instead of learning variations by rote, why not develop your 'common sense in chess', as Emanuel lasker called one of his books!"
- Victor Korchnoi - 'My best games'.
I tend to think defensively first. I like to focus on the placement of my knights when I play unorthodox players. They can be used defensively or to attack the center if he should choose to rush you. The castling of your King is also very important.
Once you are set defensively, attack, and attack hard.