I don’t really believe in superstition, segulas, ayin harah, etc. feeling that one should rather turn to Hashem in prayer. However I know there are things that are kabbalistic in nature that are important, like not standing on finger/toe nails, etc. I’m not sure what the difference is between what’s really kabbala, and what’s not. What things should we be careful of? For example my mother-in-law told me that if I see a shoe upside down, I must turn it over. While I think it’s nonsense, I find myself constantly turning over shoes "just in case". Please advise. Thanks

You are right; it is not easy to know what irrational practice is sourced in Talmud or kabalistic writings or backed by real authentic Jewish tradition and which one is totally inappropriate superstition. The only way is to learn or ask those who are learned. It is written pregnant women should try avoid stepping on cut fingernails, there is no real source for turning shows upside-down.