We just completed the car buying process (first time I have ever done this!), and honestly this was one of the most challenging questions for me. Here's how we did it: first, we culled our list for dealbreakers unrelated to safety (e.g., we needed a hatchback, we were unwilling to consider cars that averaged less than 30 mpg, we did not want a van or SUV, we wanted to spend under a certain amount, etc.) That got us a list of maybe a dozen cars. Then I looked at IIHS and NHTSA testing on each of them, and eliminated anything that did really abysmally. (We left things on the list if they had mediocre performance, though.) Then we went to go look in person at the six or so cars that were left, test drove, read anything I could find online about them, and narrowed the list to just three. We test drove again and began actually pricing our two favorites with dealers, and then just went with the one of the two that made the most sense considering all of the factors. It turned out that both of our final two were IIHS Top Safety Pick+ cars, but because we weren't looking at high enough trim levels for the safety features that added that +, it was moot. (One of our two final options was the Prius v, which failed the small overlap test last year and passed with flying colors this year after a redesign, though, and we specifically did not consider the 2014 or earlier models because of that--even though we could have gotten a killer deal on one! Part of that was unease about knowing the car had failed that test, however unlikely such a crash might be, and part of it was resale value, knowing that Consumer Reports will likely have a big black "not recommended" mark for those model years that might eat up anything we'd save on the purchase price if/when we eventually sell it.) I'd say cars fell off the list just as often for other reasons as for safety, though--it was more about the sum of all the pieces. The only car where the crash test results were the only dealbreaker was the Nissan LEAF (which I'm still a little sad about!)
What helped was continually telling myself that all of our options would be safer than the 14-year-old car we're currently driving, so there's that. (Although even there, I was surprised to find that some of the safety features we have on our 2001 car are not standard for every manufacturer yet!) It does also get challenging if you're looking at both new and used cars, as we were, and have to factor in what safety features a higher-trim-level older car might have vs. improvements to overall design changes a new car might have. Makes your head spin!