Search engines are constantly evolving to better serve users. Links are one of the major factors with search engines. Link building is the method of creating links on high ranking websites that are related to your target market back to your site. The major search engines factor in the number of quality links a site has pointing to them when determining their page rank.
Search engines look for natural results. Strive to ensure every website link is related to your niche. For example, if your website is an auto parts shop, linking to an auto repair shop would be acceptable. If your auto parts site were to link to say a wedding blog, that would be seen as unnatural. A good rule of thumb is if it doesn’t relate to your website, it’s not a good link.
Search engines seek effective results. It is better to have a small number of quality links rather than a large number of poor links. In fact, having an excessive amount of links can do more harm than good. For example, gaining 1,000 links within a month, but none of the links being related to your site is going to put you at risk of being penalized by the search engines, causing your ranking to drop drastically. Now, you have some major issues to attend to, cleaning up toxic links, and trying to get back into the good graces of the SEs. It's better to build related links naturally, for example, if you were to get only 10 links related to your niche within a month, that would be much more effective than the 1,000 unrelated links, especially in the long term. The natural links would be much less likely to get your site penalized, they would actually help increase the ranking and authority of your site. It's better to focus on quality rather than quantity when link building.
Search engines like inbound links. Avoid reciprocal links, as this method is generally a mutual exchange to increase link count. Search engines can see reciprocal links as a manipulation tactic. This is not to say that two websites can't link to each other, but it should be done so in a natural way, not as an agreement to increase link count. One-way links carry much more weight than reciprocal links, so focus more so on getting sites to link to you.
Achieving a high ranking in the SEs takes time, particularly with highly competitive keywords. There are no shortcuts to success, as they say, trying to manipulate the SEs may work short term, but the search engines will eventually catch on, penalizing you. Following search engine guidelines, creating quality content that users want, and building quality links will ensure your site is "future proof", ranking well now as well as in the future, regardless of SE updates.