Think about the material critically when first learning theory, ask yourself lots of dumb questions and try your best to resolve them.
Be patient and don't flip to answers when you are semi-sure of something, reach the level of confidence where you are almost certain of your answer's correctness before checking. (If you can't reach this level of confidence, you probably have not yet learned the theory well enough). During this stage, do difficult questions to really test your understanding.
Worry about speed and accuracy of the routine mechanical computations after you have mastered the theory, that stuff is the easy part...but if you don't fully understand key concepts then there will be very hard upper limits on how well you can do.
And enjoy yourself! Curiosity is a much more potent motivator than the desire to get a mark > X.