Boosting the PR value cannot be determined by the exact number of backlinks established. Many more things are taken into the account like the exact placement of the links on the pages, the number of outgoing links and so on.
what does it mean by quality links? Can u define properly for me? I am quite confused about the whole matter.
Quality links means the link have a good PR and it must relevant to your website.
The biggest issue which people don't care is of spamming which make their website ranking down and thus avoid web traffic generation.