i want to design my A4 portfolio like a book format. and want to design 2 pages at a time. Could you suggest how shall i go about it. I was thinking of taking pages (1,4-2,3) and (5,8-6,7) together. Since i was wondering how they would be printed and put together to be bound as a book.
First of all, as Scott said, I would never advise you use Photoshop for this kind of project. Photoshop is not intended for multiple page print projects while InDesign is designed specifically for them. In fact, InDesign has a Print Booklet feature that will re-arrange your pages upon export so you don't even have to worry about this.
That being said, regardless of what you're using to design your A4 booklet, I would set up your pages like this:
Page 1, Side 1: [8|1]
Page 1, Side 2: [2|7]
Page 2, Side 1: [6|3]
Page 2, Side 2: [4|5]