Picture 1 on top is a spread (two sides or pages facing each other). Notice, the coverage is not perfect. Remember to let each spread dry completely before gessoing another spread or the pages will stick together. Also, be careful of the edges or the edges will stick together.
While the gesso is drying, think about the theme of your book. Will be there be a theme? What materials will you use for the background? Will you use paint? Will you use paper? Will you collage using scraps, magazine pages, or other text and images? Will you use fabric? You can use fabric - create on the fabric first and then use strong double sided tape all over the board book pages to adhere to the fabric. You need to do all the art on the fabric first before adhering to board book.
One other important thing, color your edges all over the book - top, side, and bottom. I used my finger and put on some blue, then dark brown, and then some copper on my edges. Fan the board book a little to dry standing up so the pages don't stick together.
Picture 2 (middle) is of the covers. Usually, you do the covers of an AB last. I could not decide on what I wanted the AB to be about so I did the cover first hoping to get an idea that grabbed me. It also helped that I had just gotten a sample pack of Stewart Gill paints to play with. They are more for fabrics but can be used on paper as well. I did a lot of random playing with the paints. I let them dry and then used a sanding block to sand down the paint in the direction of the gesso marks. I was so groovin on the gesso marks that I decided to use them in my book. Just another texture that grabbed me. It was at this time that I decided that my theme would be "forgotten". This would be about forgotten things that could be given new life through art.
Picture 3 (bottom) is of some pink halo gold Lumiere paints that were dried, large polka dots put on the page by some paint and a stencil. Once that dried, I used the sanding block and sanded the spread down like with the cover.
That is as far as I have gotten. What do you want to do your altered board book about? BTW, if you are in the altered board book swap, this would be a good time for you to start a 2nd AB. You could do it at the same time as the first one. They don't have to be the same. It's just that you would have a finished AB to show your friends and to look over whenever you want. This way, you will not feel bad about giving away your hard work, work you slaved over every detail AB, to your swap partner. Trust me. It is easier to give away an AB if you have a similar one yourself.