Build quality links to make your site stronger and avoid all sites that possible scrape your content and outrank your own site. For new sites, your competitors are less dangerous than submitting to social bookmarking services. Keep it clean and white hat, so your competition can't knock you out with a report to google.
I don't know why you think social bookmarking services are dangerous, but you sure are wrong about new sites. If the site is new it is definitely in danger and can easily be knocked down with automated web directory registrations and huge spammy/porn site-wide links. 4-5 thousand bad quality links that appear over night can possible do permanent damage to a new site. My suggestion, don't get into such a war with your competition. Behave and you will most likely not have any problems.
Sites that are in competition usually agree to follow white hat tactics in competition..as they know that any blackhatting will end up imploding their entire niche' , since everyone would fire back. Black hatting your competition - Rules: ------------------------------------ Similar to thermo-nuclear war. If anyone pushes that button, they all push it in response. Co-existence and competition through less dramatic and drastic means