Dish soap and warm water.
I bought my friend a non-dishwasher-safe mug from a charity shop. It's a bit dusty and dirty, I was wondering what the best way to wash it might be, please?
Soap, water and a dish sponge.
A paste of baking soda, dish soap and hot water.
Soak it in a sink full of dish soapy hot water. Then hand wash it.
Soap and water!
Dishwashers are excellent sanitizers if you have one.