The only way to improve your reading is to practice.  A few simple techniques can really help, ideas such as:

• If you don't already do it now, then start to read quality newspapers and practice noting down the key words (not the whole sentences) of each article you read.
• Read text faster than you would normally do and see if you still get the overall meaning.
• Read books that are more academically challenging than you would normally, but choose a subject that interests you, or a hobby – otherwise when the going gets tough you may just give up.