Well, according to the MS JobsBlog (blogs.msdn.com/jobsblog), developing yourself into an STE is hard. Even though courses are taught at Uni / College, generally they aren't adequate enough. Obviously after 2 years you're good at what you do. What helped you get to where you are today? What advice would you have for STE candidates?
In my case (I started out as an STE, was a tester for 2.5 years before deciding that PM was where I belonged), I got my tester job because of my sysadmin background. As a sysadmin I was always solving problems, and narrowing down where the problem was. I fortunately had a skilled interviewer who asked me questions about systems administration that were really questions about testing, such as “A user reports that they can't connect to the network. What do you do?”. Those narrowing down skills were really useful to me as a tester. Also, when I was a tester in Outlook, I ran our interoperability lab, so my skills with various operating systems/mail servers were tremendously useful to getting me in the door.
I'm sure luck played a big role too - lucky that the job I was randomly assigned an interview for had something to do with managing servers (which allowed me to use my existing skills there while I grew my software testing skills while in the job), lucky that my interviewer was skilled and asked me good questions, lucky that I was offerred an interview in a group dealing with a technology I've long been interested in (email), etc.
Of course in my case, I was mostly a UI tester (but this does not mean that I just click-click-click-it's-real-easy-man on things all day, I'm pretty defensive about that, but that's a story for another time). This experience may not apply to an SDET.
Like all jobs here, you have to be passionate about what you do, and that passion needs to come across in the interview. And I did (and still do) loooove testing. Some of my best days at Microsoft were spent having fun tracking down tricky bugs; I love the thrill of the chase.