Realizing you won’t be able to test everything – how do you decide what to test first?

There are a situation where testing a new build is allotted a bare minimum time, or you are given several tasks or projects to look into. In such case, where you cannot able to completely cover all the scenarios of testing, you can focus on main functionality and features released and check if any critical or blocking defect should not be present in an application during regression tests. Usability, functionality, security, performance are few testing that should be carried out either using scripts automatically or test manually.