There aren't any standard procedures to my knowledge. As with most things, once you get more on the business side of the process, different companies and different individuals have different practices.
I've done work with a company, which was a little more on the continuous work/marketing side for clients, have a clever system, where they give their clients a login to their website, which takes them to a page with all of their resources on it available for download. This was more geared to copies of their logo and other misc works in different color formats, resolutions, and file formats, so companies without a design junky could grab different variations of it, or a vector file if they needed it for any reason. You could do something similar to this, have a log in which displays images, and notes on the work in progress.
That's a pretty heavy procedure though. If it's a smaller, one off gig, you may just want to consider compiling your images into a pdf file with notes explaining what's what, where you or they are in the process, what's needed from who, and what comes next. Slap your logo at the top and format it nicely, and it will look more professional than simply attaching images to an email.