What is the best way to increase my typing speed in a small period of time?

I do not type correctly. I purposely never learned. But, I have my own way of typing, and though I make a lot of mistakes that I need to go back and correct, I type fairly quickly.

I might be starting a new job in a few weeks and my typing is going to need to improve. Do you know of any ways I can increase my typing speed quickly. I know I’d have to learn the correct way to type to really be quick, but I am just looking to increase my speed by maybe 15–20wpm.

Any suggestions?