If you take a look at the vocabulary learning principles thread you should note well reading fits the ideal way to learn vocabulary:
1. Vocabulary is learned incrementally (multiple exposures)
2. Learning requires multiple contexts
3. Vocabulary processed more intensely will be learned better (the depth of processing notion, or learning involvement)
4. Vocabulary is learned through spaced exposures and not fewer massive exposures)
So reading stuff with new vocabulary in it is good for you, but how much new vocabulary? You should understand more than 90% of the words when you tackle a new reading - if you understand any less, you might have trouble getting the main idea of the story / article / whatever. Since vocabulary is learned in context, you must understand the reading to benefit from the exposure to new words.
So find something that's fun to read and that you can understand. Do a lot of reading this way and you're vocabulary will increase (gradually).
