The natural one-way links.
This one is solely based in good content and resources. This is the safest method of link building available as far as search engines, which look at the “intent” of links. But it is also the slowest. If your site is new, then as part of its launch, submit it to niche web directories. Start with a few highly trusted directories, but do not have more than 10-15% of your overall links coming from them.
Don't overlook industry-specific directories that may be paid or unpaid. These usually send highly qualified traffic and can be a real bargain. Directories will get you site many natural one-way links, at a natural speed of growth. This combination of type and speed is very beneficial. Look for sites that would benefit from offering users your content.

Linkbaiting, or link bait.
This one is not easy, and involves creativity. But it is worth every effort. Linkbaiting refers to content, videos, images or anything on your site that is created with the intention of increasing links to it. It is highly effective in getting links, probably the cheapest too, based on the cost of the “bait” you use, has no negative effects from the search engines, at least not for the moment, since all links generated look natural. When complemented by social bookmarking, the networks associated with these links will add even more value to them.

Paying for links, or paid links.
These links can have great short-term search benefits. These are good mainly for sites that have tons of pages with content, and have been well established online for years. In addition, these sites also have tons of natural links to them, again because they had been well established online for years. These are not recommended for new sites. Look for sites that are highly on topic with yours, and in complementary niches. A very important factor in the evaluation of these links, like any other, is age. And the latest “Google Slap” effect were sites fall pass the top 30 in the listings, is affecting primarily those which do heavy link buying.

Bad links and their effects.
Outbound links play a big role in the way search engines determine who your “neighborhood” is. Bad neighborhoods will affect your search engine rankings. Things like FFA (Free For All) link pages, links farms, etc, fall in this category. Note that this has nothing to do with your pages going into the supplemental index. That is not the kind of penalty these links cause for your site. And the amount of bad links considered is a big one. A small amount of them would not trigger a penalty, but make sure that your site is not related in any way to those link patterns.