Google insists on the concept of spontaneous linking. Users who have visited the site remain fascinated by the content and insert a link in their site, or blog. Nice, but there are certain types of sites that nobody wants to link. Let’s take for example those dedicated to online casinos. The competition would never think of linking a rival site. The players, to whom the site can really like, are interested in the game and do not have their own resources on the net where to link. Maybe someone mentions you from a forum, or some social media, but even this is not very likely. Therefore, if you want to survive you have to work hard. But the work must be very intelligent: Mr. G. must have impression that there are others who link you and not that you personally produce auto linking, to get more external links. The main order is to diversify as if it were done by many other people.
What does diversify mean? Reading a bit here and there and having some experiences of my own (21 years as webmaster), I will try to list some stuffs on which we must be careful. Let's start with the keywords connected to the links. If my memory is still good, the rule about keywords density was introduced at the beginning of 2012. The thought was: if many people link a site spontaneously, the title, i.e. the keyword with which it is linked, will vary. Investigating the sites that looked good and authentic, the staff of the most famous search engine in the world came to a conclusion that at most 50% (approximately) of the titles used can be equal. In that period, I have heard on my skin the introduction of this rule: my numerous sites have lost many positions on Google. The people that following development of Google’s procedures had a great reaction and they were able to quickly understand the problem and the spread of information was fast. Today I try to keep my main keyword at 40%, to have a margin of safety. If you are very close to the limit, just lose two or three links you can overcome the limit and be punished for that. The links that use the site's address as a keyword are very important. From my experience, you need to have a minimum of 5% of these titles, but I try to stay even on 10 or 15%.
Another necessary diversification is to have a certain percentage (I am inquiring about it and I do not know at this moment to express a number) of the nofollow connections, i.e. those that do not pass PageRank. This is part of the spontaneity: not having any link with nofollow, since this mode of linking is quite common in the network, puts the doubt to Google that all links are created by the same person. Be clever and simulate spontaneity, always. There are also other small tricks. I find it quite productive to link using the address as the name of the link and inserting in the code the tag "title" with the main keyword. Not always, to leave the feeling of naturalness. This is even better if you are linking with an image. In this case, I also exploit the "title" and "alt" tag of the image itself. Another trick that I apply is to use the address, where possible, with the different syntax. For example, sometimes I use “http://my-site.com/”, but sometimes I omit the slash, so I have “http://my-site.com”.
The last thing. I have many blogs I use them to link my main sites. Not that I fight for the position but having a good one creates a bit of traffic and also gives the possibility of getting a few clicks to those places that can produce some profit. Analyzing lately some of them, I noticed that it is not enough to have the links with the keyword, but also in the pages the same keyword must be present. If not, no placement at all. This rule was introduced to avoid the unpleasant inconveniences that for some vulgar keywords comes out on the first page the site that has nothing to do with it. You will remember that several years ago, looking for certain shameless words, in the first place came the website of the American president, not much loved by his citizens. From now on, I will insert the necessary keywords in the texts I post. Indeed, in some cases I have resumed certain posts and corrected them, adding the keyword in the article so that it looks all natural. So, remember and repeat the catch-phrase: spontaneity and naturalness.