You're Not Using Different Cutting Boards
It might come as a no-brainer to you and me, but some people don't actually switch or clean cutting boards after cutting meat on it. Chicken is literally poison if you don't treat it right. You could end up in the hospital if you don't properly sanitize and separate raw ingredients.
You're Buying Pre-Shredded Cheese
Shredded cheese at the grocery store is very convenient, but a lot of the time they have to coat the cheese with starchy powders to prevent the cheese from sticking together and spoiling. It's always best to buy a block of cheese and shred it yourself if you can.