It is important to learn strategies for determining meanings of unfamiliar words without looking them up in the dictionary. why?
looking up every unfamiliar word in the dictionary increases your reading speed.
you may face certain instances in which a dictionary is not available (such as on standardized tests).
it is not actually important to learn these strategies.

The correct answer is the second one, because it might happen that you do not have a dictionary at hand and you need to know the meaning of an unfamiliar word. So, if you develop some strategies, that will help you immensely. 
The first option is incorrect, because quite the opposite happens - it decreases your reading skills if you have to look up a word every 5 minutes.
And the last option is also incorrect, because those skills and strategies are important.