the way I store private keys
1. I use a web wallet (Myetherwallet)
2. Bookmark the web wallet site to avoid phishing attacks
3. copy on white paper, PC, MOBILE and flashdisk
4. I will not tell anyone and only I personally know about this.
We wallet doesn't safety your private key that's think you need use hardware wallet for fully safety your wallet. Before two years ago i was saving my private key in my phone book but i read many topics this not good safety, so now i only use hardware wallet for safety my private key.