You can make a little extra cash in your spare time by taking online surveys. Companies who want to know what’s on the minds of their customers are willing to pay for your opinion. Online surveys won’t make you rich, and won’t allow you to quit your day job, but you can make a little extra cash while engaging in a fun hobby.

Search the internet for companies that will pay you to take surveys. Do not fall for scams where companies ask you to pay money to find fragile lists. You can find a good one here.
Fill out the screener surveys. Many survey companies offer screener surveys when you register, which usually don't pay. But it's worth the little extra time it takes to fill these surveys out, because the more demographic information the market research companies have about you, the more targeted surveys they can send you.
Check your email for survey opportunities. The companies you signed up with in step 1 will send you survey requests – some more often than others.
Choose and complete the best surveys. Now that you have lots of surveys, you can pick the ones that seem the most interesting and most lucrative to you. If you have time, do them all. If not, decide which ones you’d like to take. You're under no obligation to complete any surveys if you don't want to.
Earn a little extra money. When you take the surveys, the company will specify what you’ll receive as payment. Many companies pay in cash. Some offer prizes or products. Many companies let you accrue points which you can trade in for cash or prizes.
Be wise. Some websites say you won a xbox360 or a new laptop for example. There is usually an asterisk near the "you won" part. This means you have to do something like buying stuff before you even get to talk about your prize. Don't fall into these sorts of traps, they're ridiculously difficult and not worth it.
The more companies you sign up with, the more survey requests you’ll receive in your email and more opportunity you’ll have to make money.
Make a dedicated email account set aside just for surveys to keep junk mail out of your normal inbox.
Any individual survey site may only send a couple of surveys to you in a given month. The more companies you sign up with, the more surveys you'll receive.
Most of these sites have their own 'referral program' which adds more to your earnings. The more people that you refer to that certain site, the more incentives you will get. You can get some goodies here: 1, 2, 3, 4, 5

HELPFUL TIPS FOR STARTERS LIKE ME
Always check privacy statements. Who will your information be shared with?
Never pay any site to find these survey sites for you. Search the Internet for free by yourself.
Do your research.... Some survey companies only award points or enter you into a sweepstakes for completing surveys.
Teenagers can also participate in this but you should always research whether or not a company allows teens to participate.
Many websites with online surveys often have spyware and viruses, so be careful of them.
Dont accept what sounds to good to be true sometimes
You get like $1-$50 a month mainly from doing online surveys
Most survey sites (and their affiliate companies) will start sending you tons of spam. Before you sign up you should get a separate email account (Yahoo, Google, Hotmail and others offer free services) and use it just to sign up. Should you get a lot of spam it won't clog your regular email. Look for an email account with excellent spam filters and junk mail options.
Also avoid giving your phone number as it can open the door for telemarketing. Some can even circumvent the Do-Not-Call lists because you've signed up to receive information.