In our project,each fields and properties whose modifier is PUBLIC will be serialized as a string format.Of course,we could modify their modifier to INTERNAL ,even PRIVATE,to prevent to serialize the fields or properties you don't really want.But in some certain situations you must to make a data modified as PUBLIC,we can also use the following changes. 
I added a custom attribute("NonToJsonAttribute") in project,and use reflection to avoid adding fields or attributes to a serialized collection.By this way,every fields and properties that marked with "NonToJson" attribute will not be serialized.
Below is the example-code:
interface ITest
        {
            int TestProperty { get; }
        }
        class Test : ITest
        {
            //The property what I want not to serialize
            [NonToJson]
            public int TestProperty => 0;
            public int Other { get; set; } = 1;
        }

        . . .

        Test t = new Test();
        string result = LitJson.JsonMapper.ToJson(t);