Don’t blow chips into the spindle! Do not blow chips during a tool change. And when you are blowing chips, don’t blow them towards the tool carousel. Chips in the spindle will cause bad finishes and out of tolerance parts. Keep an eye on your holders and keep your spindle clean.
Visually inspect your parts. The majority of problems with machining will be reflected in the part coming out of the machine. Are the holes off-center? Didn’t clean up on one side? These are things that need to be caught at the operator level.
Stack your parts neatly. Unless you are throwing hundreds of parts into a box to be weighed, there is no reason to not stack your parts into rows and columns. It makes it easier for anyone to get a quick count of the parts, and if there are problems they can be tracked down to the first non-conforming part easier.
Building on the last tip, keep your area clean. There is no excuse for soda cans and candy wrappers on the work bench. Throw broken tools into the broken tool box, and keep the chips off your bench.