It depends on the level of competition of the keywords that you are using. Better to check that first before to do any link building method for you to know how hard you will work for your site's ranking.
It all depends on the competition for the keywords you are trying to rank for, some may have millions of backlinks, and very PR, so it would be impossible to out rank them in a short length of time, others have very few backlinks, and a PR of 0 or undefined, those are the ones that is feasible to outrank them in a short amount of time
For now a google updated his algorithm , you need create unique account. and create quality backlink.