Context Clues - When you read a word that you don't understand you can usually determine the meaning by reading the sentences the word is in, as well as the sentences around it. 

Example: I couldn’t believe it. I got my paper back and was shocked by my grade. I had received a D on my essay. I thought I would get at least a C, but was hoping for an A. When I asked my teacher about it she said that it was an erroneous mark and apologized. I was grateful to hear that. She incorrectly wrote a D when I had really earned a B on my essay. I’m glad I asked and didn’t walk out of the classroom upset.

In this example we learn that erroneous means incorrect.  We learn this from the sentence that says "She incorrectly wrote a D when I had really earned a B on my essay."

To enhance your understanding about context clues and practice being a word-detective visit this interactive site.

Here is an example of a quick way to learn a new word. Personally, I learn new words all of the time when I use this chart during my reading.