Study Strategy
I began by answering the sample test questions available on the TEA resource pages (found under "Music EC-12 Study Guide" and "Music EC-12 Overview"). Those aren't the exact link names, but can be found on the TEA website. These are PDF guides that have sample questions with correct responses and rationales. I also found sample test questions on the TMEA website with listening examples. I suggest taking these sample tests before studying to identify weak areas that need to be revisited. The theory questions were not too difficult, but I would review intervals and instrument transpositions on the (amazing!) interactive website Teoria.com.
Testing Strategy
The 177 Music EC-12 was easier than I expected, but there were some challenging questions about instrumental techniques. Most of the questions dealt with band, but there were a few vocal range questions too. I suggest reading the Music EC-12 overview before studying; this explains in detail which domains will be covered in the exam. Listening (25%) and Classroom Performance (25%) carry the most weight.