How did the invention of the printing press affect literature during the Italian Renaissance?

Before the printing press was invented the only people that could afford any type of book were very rich people (not that there was a ton of literature at this point). The printing press made books more affordable. But even bigger than that was the boom in literature created - before the majority of ALL literature had to do with the Roman Catholic church. Monks re-copied entire works - the most popular being the Bible, it would obviously take a very long time. Not to mention it would have been written in Latin. It wasn't until the printing press and Martin Luther came along that the Bible was out in languages OTHER than Latin.
When other could read the Bible for themselves that is when they started disagreeing with the church (Martin Luther - who translated the first Bible into German, started the Protestant Reformation with his 95 Thesis).

Still at this point, not everyone could read - but those that could were clamoring to read more and write too. The more that was published the more the ideas were spread through the country. I would say that the printing press was a big factor in the Italian Renaissance.

Hope that helps - if you need anything else - let me know