Hi Dreamer or anyone ...

If we never tell the company our expected salary -> if the company/interviewer ask, what is your expected salary?  How to answer?

If we say "let you offer me", the interviewer might say "How come you can't value yourself?" -> don't you see this as we actually de-value ourselves because we ourselves also can give us "a value"?

If the company say "OK, we would like to offer you RM4000 (previous salary is RM3800, etc)" -> if the offer is not within the value that the interviewee wants, what should be the best method (the way to say) so that we can make "counter-offer" -> I mean ask for more 

Thanks in advance.

I guess this answer would be last resort. I guess the best thing to do is to do some research before your interview session.

Besides, if you unsure of what is the expected salary range, just add 30%~40% of your current salary

Inside the application form, didn't they ask you to state your current salary?

As for research, you don't need to have friends working in that company to know the salary offered by them.