Computer security is wide ranging from the almost old-fashioned but practical advice of keeping your computer physically locked away to network access control to encryption of data on websites and in communications.
The menus here offer a selection of areas of interest to a smaller business.
Larger businesses will be tied up with audit checklists and ISO’s and whilst very important did think of this quote from Cybersecurity and Cyberwar (what everyone needs to know) by Singer & Friedman P233:-
“This focus on compliance can turn security from an iterative, adaptive process to an organisational routine disconnected from the risks faced. Compliance replaces accountability, since organisations can avoid any decision that might improve security”
A more rigorous approach is to follow the Centre for Internet Security 20 Critical Controls. The first five eliminate the vast majority of your organisations vulnerabilities.