Tips for Reviewing Code

Hello all. I work on a small team and I’ve been tasked with taking on the bulk of code review for when my senior goes on leave. Although I’ve read a fair bit of code (man am I lucky I learned to code before AI “got good”) I can’t say I’ve done a lot of actual “review”. Does anyone have any tips? I feel responsible if anything breaks after I review it so of course I want to avoid that.