Are you good at English? If not then you're going to have to work really hard. Media Studies is an essay-based Higher and you likely won't be taught a form for how to write them. This is different from some of the other subjects, eg Modern Studies - where even at Higher they will spend time drilling the essay writing skills into you.
There are three units: fiction, non-fiction and production.
Fiction and non-fiction are both text-based units and whether or not you like the units will likely depend on whether or not you like the texts. We studied a YA film, Small Faces, for the fiction unit and a short campaign video (this one!) for non-fiction.
For production my group produced a documentary on a number of venues in Glasgow (for cinema, gigs & nightclubs) over eight weeks: three for pre-production (planning); three for filming; then two for post-production (editing). I don't know how it's dealt with in other colleges/schools though.
The exam includes writing three essays in three hours: two are sat on the official exam date (40 marks each) and the third is sat whenever your school or college decides (20 marks).
The 20 mark essay involves analysing a magazine cover (at least I think it's the same everywhere!). In truth, there is actually an hour and a half for this exam - but the first 30 minutes are for planning. Try writing early and you'll be asked to leave. More than the exam, the preparation for this essay is tedious as hell. We were made to write eight practice essays in six weeks in preparation! At least five or six were homework.
The first of the 40 mark essays involves analysing a text you've studied in class.
The second of the 40 mark essays will either be based on your production experience or involve planning an advertisement (or at least that was this years question, I didn't do much on that area of the course so I don't know if there are other questions that can be asked).
There is a lot of writing to do in a short space of time: you are expected to be able to produce approx. 1,200 word essays in an hour. You are graded on content in three key aspects in each essay and if just one key aspect is failed then it can cause the entire essay to fail. There is a lot of terminology to remember and if you don't like the texts then it'll be fairly boring. It's obviously not the most difficult Higher but you still need to put in the effort to do well. You need to know the texts well, just like in English, to succeed - but the exam questions are much more predictable in Media Studies than English, which makes it seem much easier in comparison.
In short: go into it thinking that it'll be easy and you'll be disappointed.
However, on a more positive note, it is an interesting Higher and you do get to sit around watching TV/films in class until the hard part starts. It's also quite a social class - there are lots of opportunities for pair/group work, especially in the production unit. With that in mind, it's easy to start to thinking of it as a laid back class - but if you let yourself fall into that mindset then, like with other classes, your grades will slide.
More importantly, what are you planning to do post-Highers? Media Studies isn't the most respected Higher, so you might want to keep that in mind if you have certain uni/career goals in mind.