Practice looking for a deeper meaning in the things that people do and say or material that you read. Know that the speaker or author may have an agenda other than presenting the facts. Do not accept things to be true -- or false -- until you have analyzed the information and found factual support.
Ask questions to support and extend the knowledge you already possess. Seek out reliable sources of information -- experts, non-fiction books -- to help develop your critical thinking.
Examine the reasons for existing situations. Take note of your surroundings and look for opportunities to figure out why something exists as it does.
Keep your emotions separate from your critical thinking to avoid illogical patterns of thought.
Acknowledge that there may be more than one way to accomplish something and analyze the situation to find it, even if your experience tells you otherwise.