First of all, it is important to be familiar with the term "SEO" (Search Engine Optimization) which is nothing more than positioning our information in the organic search done in the browsers.
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SEO is not the same as SEM (Search Engine Marketing) since the latter is a paid system (PPC or pay per click) which can generate results in the short term.
The "keywords" are a group of words that define what a content is about, thinking about what the final user would look for when browsing the web. If the search engine considers that our keywords define what the beneficiary is looking for, then the results will appear in the first searches.
The most important key factor is to place well the "keywords" to facilitate that our content appears in the first results of the searches, for this you must take into account the synonyms and keywords related to the main tag you want to position. It is important not to use them in excess by abusing the tags, on the contrary, it is better that they are coherent and concrete.
It is not necessary to use the "keyword" alone in each title, it is enough to use synonyms and related words. For example:
If the keyword is YOGA we can use it as follows:
Title: Yoga for health, why is it so important? Subtitle: Advantages of doing yoga Subtitle: Why yoga is so beneficial for health?
In the title the keyword has been at the beginning, that is something important, we must take care of the details and check that the title makes sense.
When uploading an image we must also name it with the "keyword" or with the title of the post.
Another important point is to place the keyword in the URL address also in subpages or directories. Example: http://yogasaludable.com/es/yoga/para-la-salud
We will also use the keyword in the meta title, that is, in the HTML tag with which you name each of the pages of a website and in the description without using many characters otherwise not all would be displayed only a few ellipses.
Positioning your post with keywords should not be so complicated, just use these strategies that give results in the medium and long term, be consistent and practice using them. The important thing is that little by little our organic positioning will improve with practice.