Select the default privacy setting for posts

Head to your privacy settings, and scroll down to "Control your default privacy." Here, you can select the default audience for all your posts: Public (everyone on the Internet), Friends (all your friends), or custom (exclude certain friends or lists).

Tip: If you frequently post content you'd rather keep private from a certain group of people (like your colleagues), create a list of all those people and exclude them by default using the "Custom" option in this privacy setting.