How competitive are summer internships at Uni?

I have heard a fair bit about summer internships and that students usually participate in their penultimate year. So, I was wondering how competitive they are at finance firms or engineering firms and how people manage to secure such internships i.e. what type of experiences do they usually have on their CV (maybe previous work experiences?), is the interview part more important or references, when do people start preparing (the term before, first year, even sixth form?)

I would really appreciate any guidance on this, thanks 😊

Engineering firms can be quite competitive, and there are comparatively few internships compared to graduate roles. Often candidates will have projects from university (as part of the course and/or as an extra curricular, for example Formula Student), and sometimes part-time employment. The interview is the most important part - references are usually only taken once an offer has been made. Start "preparing" as soon as you can by obtaining useful and valuable experiences you can add to your CV so that you have more to put in it than just your degree, and start applying as soon as internships are advertised, which can be as early as now.

Thank you so much for replying, just another quick question: what do you consider useful and valuable experiences? Maybe some examples?