First by signing up with them on there site they will email you surveys when available. Second you can follow them on Facebook and fill out a survey whenever they post up upcoming surveys. Third you can call to see if they have any surveys available at the moment. Lastly you can only do their surveys every three months or so. I hope this was helpful.
The answer by Porscha C is the best and it's all the info you will need
How do i sign up. Nielsen
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