To always open links in new tabs:

Choose Safari > Preferences.

Click General.

Next to "Open links from applications," select "in a new tab in the current window."
In the Safari General preferences, you can specify that clicking a link in an application will open a webpage in a new tab instead of a new Safari window.
Choose Safari > Preferences.
Click General.
Next to "Open links from applications," select "in a new tab in the current window."
This setting applies to links found in other applications, such as email messages and text documents. To open a link found on a webpage in a new tab, press the Control key while you click the link.