When you get links to your website they should be useful to users. Inbound link building campaigns have been very popular in recent years. Simply having a campaign where you massively build links to your website will no longer help you very much when they are not useful to users. The links to your site should be natural and help people on both sides of the link. Guest blogging is a great way to get links to your website. Simply contribute useful original knowledge on another website and get a link back to your website if that link relevant and useful to their users.
It's common sense. Say you have a website for a plumber. It wouldn't make sense to have links on your website that are about computers. That would be silly unless that link for computers specifically had something to do with software for plumbers.
There are many types of inbound links that you should stay away from:
These hubs for links grew rapidly in the past when spammers were trying to trick the search engine system to falsely optimize their websites.
These are considered scams that webmasters use to get more links to their websites. Web rings usually involve a system of link exchange that are pre-determined for the basis of increasing inbound links, but are not created necessarily to improve user experience.
Purchasing links on another website is not considered to be natural. It's ok to advertise on another website that is relevant to your own. I am saying just because Google has it's own advertising program called Google Adsense, that allows content providers to have advertisements on their website where in return they receive compensation. It's basically the opposite side of Google Adwords, but for content and not search. Anyways, purchasing links won't really help your SEO efforts. At least they supposedly won't help you.
Often considered to be beneficial to mutual parties, link exchanges do not always offer good value to users. These exchanges are made based on the gain of both websites involved are not usually based on merit, at least in many common circumstances. Avoid forms of artificially trying to inflate the worth of your web pages and others.
Basically any type of link that is not natural should be avoided. Don't spend a lot of time trying to buy links, exchange links and do anything that is artificial. Write great content on your website and on other websites and you will get plenty of links. You get what you put in. It's like karma. If you follow these rules then you will find that your SEO efforts will have the highest amount of success.