I wrote an article about this a while ago that includes all of the basics: 5 Steps to Prevent Your Bike From Getting Stolen in China
Always follow those steps and I think you’ll be fine – basically every theft I have heard of or experienced was due to being lazy on one or more of those. Another one that I mentioned but probably didn’t put enough emphasis in is to always lock your bike to an immovable object. Bikes get stolen in huge numbers in Chengdu but 99% of bike thefts are due to owner fault – you just have to be constantly vigilant.
For me, my bike is usually either in an attended parking lot or in my actual apartment. It’s almost never anywhere else, I rarely even lock it up outside even though I have a badass Abus lock which I got from Natooke. Take no chances!
I slipped up earlier this year and had a really nice bike stolen from right outside my door because I got lazy and complacent. The trick is to never take risks and always remain vigilant.