The verb Precisar is a lot like gostar in that it gets followed by a "de" -- BUT, unlike gostar, not all the time. The de is there because you are literally saying I need of something.
Here is the rule:
If you're talking about needing a person, place or thing (ie: a noun), always, always, always use the de.
If you're talking about needing TO DO something, leave it out.
Look at how these examples change:
And if the de is followed by an article, o or a, they contract like this:
de + o = do
de + a = da
Often, in casual conversation you can leave out the de like this:
Do you need some money?
Não preciso me drogar para ser um gênio;
Não preciso ser um gênio para ser humano;
Mas preciso do seu sorriso para ser feliz.