Links should be self-explanatory. People need to know clearly where the link is going to beforehand.
Links to content contained within the current domain (internal links) should always open in the same window (target="self" - the default setting). Links to content contained on another domain (external links) can be opened in a new window (target="_blank") if this is deemed beneficial to the viewer. Bear in mind the user can decide to open any link in a new tab or window by right-clicking on it.
Describing links correctly