Hi, I'm a year 13 student and I've applied for electrical and electronic engineering and received all offers from the unis i applied to so I'll try my best to tell you what I did. If you're set on electronic and electrical engineering, I'd strongly suggest buying an Arduino Uno microcontroller and doing some small but interesting projects on them. It gives you a head-start on programming and shows wider interest. Engineering related work experience may be helpful but its really not essential and none of the unis expressed much interest in my one week work experience with an engineering firm. I would strongly suggest going to taster days / masterclasses / university lectures as not only did it help strengthen my interest in the subject on my PS, but it really confirmed to me that I wanted to study engineering (its very difficult to know otherwise as you've never really been taught it before).
I'm also carrying out an EPQ (not all schools offer it) on the future of electronics but this is a seriously big commitment and it's not for the light-hearted, I'm kind of thinking now that there were easier ways to express wider interest, so although I'm not advising you against the EPQ, make sure you know what it will take to do it and that there are plenty of other ways to strengthen your application. The higher standard of unis tend to care mostly about your grades so be sure to work your hardest in AS levels as grades are more important than anything else in my opinion. Don't do what I did and stress that you haven't done enough compared to others applying for the subject such as summer schools and taking part in engineering competitions. Although those things do look really good, as long as you show you have a strong academic ability and you can fill your PS with lots of examples about what you've done in your own time to express your interest then you have as good a chance as anyone else with getting into a good uni. Universities are looking for 1) academic ability and 2) enthusiasm to work hard and achieve in the subject. Bare in mind others may disagree and have their own perspective on the matter but this is what I can give you from my personal experience.
Hope this helps and let me know if you have any more questions.