I want to send few merchandise like clothes and shoes around 30kgs from Beijing to India/mumbai.

Well, I need to tell you that the maximum package limitation is 20kgs. Thus you need to send it into two packages. According to the expensive cost of air parcel, you are suggested to use surface mail.
The fare is CNY 375 for 20kg and CNY 235 for 10kg. Generally speaking, the delivery time is around 30 days.

Thanks a lot for answering my query and helping me with suggestions. However I have one more few more questions on same topic. 1) which is best and cheap surface mail service company and 2) do I need to pay custom fees for or courier will take care of it. How it works ?

You can choose China Post. It is regarded as a reliable international express company. Generally speaking, you don't need to pay the custom fees. For more details, you are advised to consult the staff of China Post. :)