I started off by making notes of what I have done related to my subject e.g., books I’ve read, webinars I’ve been to, online courses I’ve done, extra curriculars, etc (you don’t have to have done all, or even any of these really, it’s very personal and dependent on your course/goals). From this I was able to start grouping together what I had done and create a way of making my personal statement flow. For mine, I started by questioning why people study this subject, and if it should be studied at all, then answered it (obviously by saying yes), using my experience to back this up.
I got into 5 Russell group unis - including Durham and London unis, using this personal statement and am now at the end of my 2nd year!
Best of luck!