Several design techniques can be used for the external links on web pages:
At regular intervals, verify that external links from your web pages actually reach existing sites.
The general standard for external links is blue underlined text. Try to follow this standard so that users work with known characteristics and don't have to spend time learning new, nonproductive things.
Use different colors for "visited" and "non-visited" links so that users can easily distinguish which links they have used.
If you have a page with too many links, organize the links by categories and provide short descriptions of what users can obtain by visiting each link.