I’m afraid I don’t have much involvement with undergrad admissions, but I know that pretty much any relevant experience is good to include on your PS (e.g. volunteering in a junior school, working with a charity…), as is anything that demonstrates your interest in psychology, including what you’re reading outside of the ‘A’ level syllabus (e.g. take a look at – really interesting – stuff like Khaneman’s ‘Thinking Fast and Slow’, or Alain de Botton’s ‘Status Anxiety’, or anything by Malcomb Gladwell).
If you’d like more, and particularly if you have an interest in the psychology of advertising, perhaps email me at Lancaster (you’ll find me on the website) and I can ask my colleagues in admissions what would be good.
If you do come to Lancaster, do drop by and say hello!