Hi there, I applied to study a Degree (BA hons) in Fine Art at Chelsea and my offer was recently upgraded to an Unconditional one. My portfolio went down really well during the interview stage and my main bits of advice (based on my personal experience) would be;
1. Have a good variety in your chosen works. For example, I had pieces which covered photography, sculpture, painting using different medias, live drawing in charcoal and pastel, print making, model making/ceramics and sketching. In pieces that were photographed (such as sculptures and models), I displayed some of my documentation of their development from start to finish, while in some other pieces I included the developmental experiments that contributed towards their making (so as a consequence, while most pages in my portfolio included one work total, other pages included a number of examples). I also brought a small sketchbook along to the interview which was dedicated to a particular project (featured) and was my best overall example of a sketchbook (the interviewer also took interest in this sketchbook).
2. Be prepared to be questioned during the interview on anything you have put in your portfolio, such as your idea's behind a piece, which artists inspired/influenced you, how you would do things differently if you did it again or what kinds of things you would do next if you did a new project on the subject (etc). The UAL like to see people with lots of ideas and a real passion for and interest in what they do in art.
3. The UAL also like to see people who can work independently, so it's really good if you can evidence independent works in your portfolio that you didn't just do because you had to do them on a course. Luckily for me, I love doing independent art projects in my own time to explore idea's and improve my skills, so I had a lot of live drawing charcoal sketches, pen and pencil studies and photography projects to chose some good pieces from to help make my portfolio stand out a lot more (in fact despite spending the last couple of years busy doing a full-time Level 3 Extended Diploma in Art & Design, just over the majority of the work I put in my portfolio were independent projects that I set myself).
4. Learn to edit your portfolio so that only the best examples of your work and processes go in. It is also good to begin and end a portfolio on a high note in terms of how you order your pieces. Make sure you also include plenty of examples of your most recent & relevent works so that they can get a good idea of where you're currently at in your art story. How you chose to display your portfolio is also important (I personally chose a professional looking A2 size black folder that had a waterproof carrier case and I mounted most of my chosen works on high quality black card).
5. In terms of writing your Personal Statement, it is really vital to develop a good one because that can unlock the door to a lot of interviews at great universities in general. Before any universities see your work, they will read your Personal Statement first. As a college student, I attended 2 talks at my college on Personal Statement writing plus another one (which included a portfolio development lecture) at a university. I also ran my Personal Statement through with multiple people and edited it as I developed it more. None of this stuff was mandatory, but doing all this allowed me to develop a winning Personal Statement and art portfolio as well as allowed me to develop some confidence for the upcoming interview processes ahead at universities (I applied for 5 total, but I'm particularly happy with my UAL offer as that was my no.1 choice!!). Irregardless of what you read about art portfolio development etc, if you can attend any talks on the subject (many universities do them for free) then I'd really recommend that.
6. Make sure you also research plenty into your chosen course (plus other courses available at the university) and check the campus out (you would be surprised at how many people don't do this!). The UAL offer a huge variety of creative courses and during the interview I was asked why I had chosen my particular course VS certain other courses available at the university (and because I had done my research, I was able to give a considered answer to the question). Scoping the university out in advance during an Open Day also not only helped me decide in advance that the UAL was definitely the right place for me (I ended up getting a lot of offers from great universities to choose from but attending Open Days and other events at universities REALLY helped me narrow my options down), but checking out the site in advance also helped calm my nerves a bit when the interview day came because the environment wasn't so unfamiliar to me and it also helped me answer some interview questions much better (such as more specifically what attracted to the university). Scoping out a university in advance as much as possible will also help you plan your interview day better (how long will it take you to get there and where will you need to go? Etc) plus in getting to know the area in general, you may discover other things about the UAL that really attract you to it (such as the wealth of nearby top class art galleries).