We have two new ileostomies in my building, and most of us are not very versed on changing colostomy or ileostomy bags. We seem to always have a mess when changing the appliance. Have any tips?

Having an ileostomy myself, I know what a problem this can be. The more careful you are when changing the appliance, the longer it will remain in place with less leakage. 

Try to change the appliance later in the evening or early morning before food and drink are being consumed. But if you can tell the resident not to drink or eat for an hour so you can change the appliance, that also will help. If the resident drinks juice or soda, which contain sugars, the bowel pulls water in from the body when sugar is introduced, and produces more output. Keep them NPO (nothing through the mouth) for an hour, which will slow down output. 

I also have heard from friends that they eat a couple of marshmallows before attempting to change their appliances, and they swear to me it works! I have not personally tried this trick. Get all of your supplies ready before removing the old appliance, if you need to cut the appliance to fit the stoma, do that, and get your paste or seals ready to place around the stoma to keep any leaks from occurring. 

After you remove the appliance, cleanse the skin, being careful not to use lotions or creams where you want the appliance to stick. Personally, I clean my stoma area with an alcohol wipe to get a great adherence. After you apply the new appliance, put your hand on it to warm it up for better adherence. You can even use a blow dryer to warm up the area to get the appliance to mold to the body better. 

Baby wipes, paper towels and sealable plastic bags all will become great friends when changing appliances.