Links - this is one of the main elements of all sites, the existence and the more development of the Internet is difficult to imagine without them. A lot was said about the links, but I didn’t see that it would be collected into a separate topic, maybe I looked badly.

So, I will try to collect everything in a heap.

Link must be underlined

This is the usual type of link for a person, which allows you to immediately notice it among the text.
Not a successful use example.

In this example, the left is just the selection of the company name, and the right link. Without moving the cursor, it is impossible to determine what this selection is. With an underlined link, we immediately see the difference between the link and the selection.

the link should be highlighted in color from the main text

Selecting a color other than the color of the text allows you to immediately notice the link and distinguish it from the underlined text.

In the example, both the left and the right are a link, to the left, to distinguish from the underlined text is possible only when you hover the cursor, to the right, the link is immediately visible.
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When you hover over the link should be a reaction

The reaction when you hover the cursor on a link can be a change in its color, background and other effects. Changing the look of the link immediately focuses attention on it, just the highlighted link can be easily distinguished from other links on the page, this is especially useful when there are many links in a row.

If you hover the cursor at the beginning or end of the link (as in the example), it is impossible to understand exactly where you will get.
The list of tags to post on habrahabr

Immediately understand what you press.
I do not recommend the use of changing the font size, its thickness or tilt - because of this line start to "jump" when you hover.

Links in the menu

To the links in the menu, add a few more recommendations.
Let's take the standard situation: the site has a section “about the company”. There are subsections “vacancies”, “history”, and also some other ones. When we go to the page "about the company" - remove the link from the section in the menu. When we go to a subsection, if we don’t put a link to the “About the Company” page, we will not be able to go back (without the help of browser means); different from other links in the menu), make it fat well and other selections.

If the link in the menu opens subsections or additional options - it should be indicated, for example, use a discontinuous underscore or put some character.
Example with underline

Example with characters