When sharing an album Google uses the first image in the album as the album cover and will also display in small thumbnail form the next dozen images or so.
Clicking on the main image takes you into the image display on G+ and you have the left and right links to take you into the next/previous images in the album.
So how do you set the album cover and the dozen small thumbnail images that you wish to appear in your album share post?
Going into the album you want to share (Select Photos in the menu on the left and then Albums) choose the More option on the right and select Organise Album.
Select the image you want as the album cover and drag it to the first position. Continue dragging images into the order you wish and then click Finish Organising.
Selecting Share will now allow you to share the album without G+ creating additional copies of the images. (A current issue for photographers with G+ which will hopefully be resolved one day).
Sharing the album will now allow you to create a new post sharing the album with images in the order you want.
Although the screen copy I used above does not show the full thumbnail images you should be able to tell that they are now in the order of the re-organized album.
Don't forget that you can view my full portfolio over on my Zenfolio account at http://www.stevegillphotography.co.uk