what is the correct way to make mocks when testing a method?

I am new using mocks , specially jMock (for java). I've done some testing before but not with mock and I am wondering what is the correct way to make them.

For example, I have a service with the implementation.. so, I have this service test. At the server test I have my methods.

Lets say I have methodA on serviceHelperTest , and as part of methodA I have this

ArrayList someValues = serviceHelperImpl.otherMethod

So, as far as I know, I should mock this serviceHelperImpl.othermethod, because I don't really care if is good or not, it is supposed to return some values.

So, let's say I expect a boolean value, is it possible to do this?

public myMethodToTest(){
     mockery.checking(new Expectations() {
     {
                oneOf(serviceHelper).otherMethod();
                will(returnValue(true));


            }
        });


     Boolean myVar = serviceHelper.otherMethod();
     ...
}

I dont know if this is correct or not... any idea how mocks should be implemented on testing units?