I think there is no fixed way for somebody to teach you how to write an effective proposal as everybody has different styles on how to approach a client but I would give you one simple piece of advice, focus on what the client has written and your proposal should be all about that.
Also, don't forget to include your past experiences on that specific type of project, it will show your future client that you are not new to that task, and you will probably complete it with success.
Happy Bidding.
