I am with most people here you need 'commitment and drive' without this you're not going to get through the interview board and that's after you've proved your self in the aptitude tests! NATS in my day normally started with 2-3000 applicants per year, tested around 8-900, interview 2-300 and take on 30! Out of the 30 up to 15 wouldn't make it!
Interest in aviation?? Well it certainly helps during first few years but the youngest person on my course had no interest in aviation, didn't know the front end of an aircraft from the back and made one of the best Radar controllers on our course!
In NATS as an ATCA I was posted to London Centre(LATCC), training in Bournemouth, I was at LATCC five years. Then Bournemouth again for two and a half year Cadetship with visits to Manchester, Edinburgh and then when about to go to Area OJT we were posted out due staff shortages. Interestingly I took a 25% pay drop to train as an ATCO which in 1987 was £9000p/a I thought the starting salary of £13k, its just gone up to £17k, was crazy all these years later!!
My first posting was Sumburgh my 8th choice most people went to LATCC. After two years in Sumburgh I then left NATS as I was about to head back to LATCC(Nothing wrong with London Centre I loved the work but cost of living in west London was stupid!!). I spent 18 great years at 'home' in a none state aerodrome, showing my years there!! Which I thought would see me to retirement but in 2008 I ended up in Dubai! I have been here ever since, I hope to retire early in around 3 years after forty years in ATC(I was 17 when I joined NATS). So I have had a long and varied career during which I have loved every minute! l still cannot believe people pay me to do this!!