It is a matter of constant practice. There are sites on the net where you can practice comprehension:
Reading Comprehension Exercises - Testing - UsingEnglish.com
Advanced Reading Comprehension 2
Reading Test 1
English tests - online grammar tests, dictation tests, vocabulary tests, memory tests and reading and comprehension tests
GMAT Testing -- Verbal Ability, Reading Comprehension
It will be a good thing to obtain a really good dictionary if you do not have one already, and learn how to use it.
Student or Learner