Description on the Link: Use specific and relevant description on the link. The link description should brief all the information of the contents in it or the pages. This is very important, as the users will not waste their time clicking links after links to get the information they need. If you are using embedded link make sure that the link description helps them to predict about the destination the link corresponds.
Underlining Links: Underlining links can be avoided at some cases. It is true that the underlined links in color always states that it is clickable link. However, it is not important to have all the links underlined on the web pages. In case you have a web page with a list of menu, where clicking each title will take you to its corresponding destination. In these cases, you can avoid the links, as it will look too odd to find so many underlines on the web page.
Colors for Links: This is most important factor considering links. It is important that you have separate colors for visited and unvisited links on the website. The simple method to get this done is changing the contrast of the color. In most cases, links will have bright colors and to make it stand out of the remaining text. With that said, you can have a darker color for the unvisited links and the same color with less contrast for the visited links. This will help the user to identify the visited links.