SEM, on the other hand, costs money but can deliver very rapid results. Your website must be optimized to make sales or at least drive a customer to get in touch (GIT – in marketing terms) so you can make a sale. You should approach SEM with care and make sure you completely understand how much money you have exposed at any one time. Start slow and evaluate your results.
A great number of public networks call themselves “private”. That’s not true. If the network is advertised, it cannot be private. We witnessed cases when Google destroyed such public networks and all the websites which had used them. They are easy to be revealed due to a huge number of outbound homepage links which are irrelevant to each other. Their posts are short, and they cannot really block SEO crawlers.
Many webmasters have more than one website. Sometimes these websites are related, sometimes they are not. You have to also be careful about interlinking multiple websites on the same IP. If you own seven related websites, then a link to each of those websites on a page could hurt you, as it may look like to a search engine that you are trying to do something fishy. Many webmasters have tried to manipulate backlinks in this way; and too many links to sites with the same IP address is referred to as backlink bombing.

Getting unique and authoritative links is crucial for higher ranking in the SERPs and improving your SEO. Google's algorithm on evaluation of links evolved in recent years creating a more challenging process now to get high quality backlinks. External links still matter and aren’t obsolete, so start working on strategies to get valuable backlinks to improve your search visibility.

Search Engine Optimization