Walk me through your resume.
The number one mistake candidates make when answering this question is translating the question to something akin to, "Tell me everything you've done in your professional career in chronological order." If you approach the question this way, most of the time it results in a bloated, rambling picture of your accomplishments, even if you've done a lot of impressive things.
There is a better way. The key to nailing this question is to dig deeper and understand the question behind the question. Ultimately, the interviewer wants to know why your past experiences, skills, and accomplishments make you the ideal candidate for the hiring company. That's the "so what" implication of this question.
Once you understand the true question, answering it becomes a whole lot easier.
The first step to answering this question is to focus on your career arc. If you walk through each item on your resume in a, "First I did this, then I did this, then that, etc." format, you will bore yourself and, even worse, your interviewer. The end result is that the interviewer will get lost in details, forget key points, and ultimately come away with a muddled understanding of your unique skills and experiences. Fortunately, there's a simple solution to that: curate your experiences and articulate your career arc and experiences at a higher level.
Tactically, you can accomplish this by running through a mental exercise of picking out the three or four experiences that are most relevant to the job you're interviewing for. Look for ones that helped you build skills applicable to the job at hand, or that taught you a lesson that is relevant to the type of work you'd be doing.
Second, you’ll want to distill your experiences. Now that you've got a narrative arc in place, the goal is to highlight experiences with a high signal to noise ratio. This means that you want to cut out the fluff and filler and make sure you hit the key points you want the interviewer to remember about you. To do this, go through each key experience in your arc, whether it's a club leadership experience, a summer internship, a prior job, a study abroad program, etc., and answer three questions for yourself: 1) Why did you pursue it?, 2) What key skills and lessons came out of it?, and 3) How did it influence your next steps?
This distillation works because it provides the interviewer only with the key pieces of information. Remember, this is just a "resume walkthrough," so each experience you highlight should be a succinct teaser of all of the valuable lessons you've learned.
The last thing you need to do when answering this question is connect the dots. Once you've painted a curated, distilled version of your resume, you naturally end it by connecting the final dot: showing how the job you're currently applying for is the natural extension of this arc. It's hard to overstate the benefits of this approach: not only did you nail the question the interviewer asked, but also you've already proactively stated how you fit into the company. Given that "walk me through your resume" is often an opening question, this is a great way to set yourself up for success for the rest of the interview.
One final piece of advice: if you find yourself struggling to curate just a few experiences to highlight out of fear that you'll leave out a lot of other details, remember that this is just the start of the conversation. If the interviewer finds those resume items intriguing, they'll proactively ask for more, and that's a good thing.