Stopped by at a books store and picked two books on software requirement engineering.
1. 「要求」の基本原則, 岡大勝/三宅和之 (Oka Hiromasa, Miyake Kazuyuki, The Fundamental Rules of Requirement Engineering), ISBN 978-4-7741-4018-6
2. 要求定義マニュアル, 神崎善司 (Zenji Kanzaki, Relationship Driven Requirement Analysis), ISBN 978-4-7980-2099-0
The first one is a short book and seems suitable to grasp some key ideas quickly (more for thinking tips?).
The other one seems more for step by step, hands on self-trainings.
So I'll try to finish the first one tonite and work on the other one the following week.