Some people don’t boil their cups at all. It’s your choice to or not. But if you do, make sure that you boil it for at least five minutes.
Make sure to read through the cup manufacture’s booklet. Sometimes they suggest against certain cleaning methods.
Some other methods of cleaning are just using a mild soap and water, soaking in peroxide, denture tablets, and Milton tablets.
Personally, on a normal basis I just use soap and water before I store my cup between periods. If/when my cup starts getting stains on it I soak it in a peroxide/water mix over night. I know some people can’t use ANY soap while cleaning their cups or vaginas. They just simply wash well with hot water.