With all the time you save when you make your meal in the slow cooker, it can be just as tempting to pre-assemble all the ingredients right in the slow cooker the night before, so you simply have to pop the stonewear insert into the slow cooker before leaving the house in the morning.
Unfortunately, especially if you are using uncooked meat, you can create an environment where unsafe bacteria loves to thrive. So you should never combine raw meat with other ingredients the night before (unless it is a marinade that you are discarding before cooking).
To save time, gather all your ingredients together the night before and prepare what you can. For example, you can usually prepare all the vegetables (such as slicing or dicing) the night before, and measure out the ingredients to save time to get it going during the early morning rush.
Also read: Safely preassemble slow cooker meals, which deals with the food safety aspect of pre-assembling.