Preparation is also a key part of getting your download and installing an update like Apple iOS 9.2.1. If you are not ready and maybe just working through some issues from the last update, there is no reason to update again right now. Online you can find many step by step guides that explain how to get the update the right way.
Most of the jailbroken iPhones out on the market know that if you are set on one version, you should not download the latest from Apple. You will have to wait to get the jailbroken version of your update before you can go further. The developers that work on those versions work fast and hard and you will only have to wait a few days for it.
If you are an iOS user that is worried it will cause problems, then the Apple iOS 9.2.1 is not something that you should be concerned about. Let the bugs get worked out and go from there. Let the developers find the issues and enjoy a new version as soon as Apple gets it ready.