I was an ETA in Poland. If you are able to do so, apply in a country with a lesser-spoken language or a little off the beaten track.

I was originally planning to apply for Germany, but my adviser (wisely) told me I didn't have a snowball's chance in hell because my German, while decent, wasn't stellar. I had always been into Polish lit and history, so I started looking into it. My school offered courses for a number of less common Slavic languages, so I signed up for Polish classes during my junior and senior years. When it came time to apply I went through at least five drafts of my essays, and I had gained a pretty extensive familiarity with Polish literature. I also worked as a tutor and an intern at an educational institution at the time. I felt prepped for my interviews and like I had really done the work to make it happen.

So, basically, my advice: start early. Pick a "less obvious" country. If you're able to do so, take courses in the language of the country. Immerse yourself in the literature and history of the country. Gain relevant teaching experience. Ultimately it's kind of a crapshoot, but give yourself the best chance to make it happen, because it's a great experience.