Cleaning the interior, especially the bottom where heated milk gets burned on.

90% of all my service calls were due to machines that were not cleaned DAILY. About a third of those were for espresso machines with a steamer and the rest for auto frothers. Most Barista's don't use auto frothers as they have very little control over the frothed milk. (Heat, froth density, firmness, holding, etc.) Milk(any type) will clog a machine in minutes if not cleaned up after use. Spoiled milk will contaminate any product with curds and have a bad smell to coffee.
* Clean up after any milk usage. Seconds count after frothing milk with a steam wand. Get workers in the habit of removing milk pitcher from wand and give the wand a short blast to flush the wand and wipe with a damp towel (tower wash and sanitized often) Leave the folded (quartered fold) next to wand on drain tray where it's always handy.) It only takes seconds to perform and customers appreciate the cleanliness and professional look.
* take a tip from Bartender's; you HAVE TO WASH WITH DETERGENT! when washing glasses that had milk drinks in them. Nobody want's a sour milk smell in any drink. Milk film can only be removed with soap and water and a brush. That's why you see automatic cup washers on every bar set up. It does take elbow grease to get these cups clean.
* Harden, cooked milk (coffee to) is best soaked in clean water (detergent optional) and let it sit over nite. This is a good practice to keep everything coffee/milk stain free as everything is washed/rinsed prior to use in the morning.
* Really, really baked on coffee (left burning on warmer for several days, weeks. Will need an urn cleaner to soak and wash out several times. Check with your coffee vendor as most will just swap them out with clean ones. Otherwise ask for urn cleaner from them and follow instructions. Hot water with a tablespoon of urn cleaner for each pot and let soak over nite. wash and rinse thoroughly prior to use.
"Washa-washa!" Aloha! ukeboy57