qingsheng is currently, by far, the most annoying thing to me about learning Mandarin. I do much better by memorizing rules, and there really isn't a set rule for when qingsheng occurs. [Which, BTW, according to Wikipedia is why qingsheng is not considered a type of tone sandhi.]

The closest thing to a rule I have that if the second character is there to make it a bisyllabic word, and doesn't really add anything to the meaning, it's likely to be qingsheng.

I know, pretty weak rule.

In particular, the following are qingsheng

• Anything with 子, of course. Except when the 子 refers to something small or something related to a child, such as 電子 and 親子. But not 兒子 or 孩子, because in those cases the first character is the one that means child.
• Most things with 头, e.g. 木头, 馒头, 罐头. Although things related to heads, e.g. 接頭, are not.
• And words in which the first character pretty much means exactly the same as the word, e.g. 坏处, 情形

It's not perfect, but it does cover a lot of the cases, and allows me to focus on memorizing the exceptions.

Last year the most annoying thing to me about learning Mandarin was characters with multiple pronunciations. That bothers me less now, so I guess that's a sign of progress! I think what bothers me most about qingsheng is a feeling of hopelessness, that I will never learn all the cases. I used to feel that way about characters with multiple pronunciation, but I think now that by memorizing words, rather than characters, and improving my reading comprehension, it will all make sense. Except for truly annoying cases like 薄.