The best tip for preventing messes when using a stand mixer is to start it on a low speed and work your way up to a faster speed. If you're like me, though, you still make a mess no mater how careful you are. I've tried various ways to contain splatters and have found two ways that work well.
Drape the bowl
The easiest is to cover your stand mixer and bowl with a kitchen towel while you mix. This works great, but if you are mixing something that can stain, like berries or beets, your towel can get ruined.
Make a lid
The solution to the staining problem is creating a lid for your mixer. Simply cut a hole in any plastic lid that is bigger than your stand mixer bowl and place it on top of the bowl when mixing. You can use an old plastic lid that has lost its container, or you can recycle a lid from a thrift store for just a few cents.
Cut the hole using a pair of kitchen scissors since normal craft scissor aren't usually strong enough for cutting plastic. You want the hole to be around 3.5 inches (8.9 centimeters) in diameter so that the mixing mechanism has enough room to circulate while the bowl opening is as covered as possible.
You won't be able to get your whisk through the hole in the lid, so you will need to put the attachment through the hole in the lid and then attach it to the mixer.