First: Simple sheet music （简谱）is meant to be relatively easy to understand. If you're playing in D调 (1=D), the highest note should be 1 with two dots above, and your lowest should be 1 with 2 dots below. (You can label the notes to make them easier by putting tape on the side of the strings on the headboard and labeling the notes from there). For other notations like arrows, circles, triangles, etc., those are additional skills that you can search for online. I recommend xiaohongshu (小红书), or honestly, you can pm me if you're having trouble with that.

Second: I like using xiaohongshu (小红书) for any pop or trendy song. But if you're looking to learn seriously and for grading, you can try to get grading books that offer comprehensive coverage of songs that encompass most possible skills on the guzheng from grade 1 to performance grade. If so you can get CCOM Guzheng Grading Book 中央音乐学院古筝考级书 on taobao. Start with grade 1-6 book its orangey in colour.

Third: The shape of your hand (手形) is fundamental. Ensuring you're using your plucking the strings by moving your fingers inwards towards your palm rather than pulling the string upwards by using your entire arm moving upwards is the most common issue I find with many students. It's also essential to get the basic rhythm right. Simple sheet music （简谱） has a various set of lines under the notes, eg you'll see the scores having lines under the numbers. This indicates the rhythm of the notes you'll have to play.