It depends on your efforts, how much you can. But do not exceed the limit of link building because that kind of act can put your site in to spam.
But for a particular project do it as you can such as 20-30 bookmarking sites, maximum business directories and classified sites. Do not forget social media marketing, because that is the superior way to promote your product in least period of time.
Forums interaction also have the much scope in this field but repeating again and again do not do spamming. Keep your website clean from spamming.
Hope that make sense!