My top piece of advice? Get rid of your images or, if you must use them, put them on the right side.
I know, you're thinking "no, no, no", but be honest: when you go through your inbox in the morning, do you right click all those red boxes to see the images?
Outlook stopped automatically showing images nine years ago. You may argue that Outlook and Gmail have settings to enable graphic content, but in 2012, with viruses and time constraints, who's going to change their setting?
The only certainty of images showing when someone reads your email is on their iPhone or iPad.
A bit of technical information. Most emails have a table format. Think Excel, rows and columns without borders showing. Images are held online and hyperlinked to the email (think umbilical cord). That is why they don't show - the path to the online image is barred.
The intersection of the column and row is a "cell" and is used to keep images in an exact location.
Marketing emails normally have a row across the top - called the header - which holds the banner image. As images are barred from showing, your recipient sees an empty space and the small "click here to view images" in their preview pane. Text is shoved off out of sight.
My advice is either to completely remove the header image or use text instead. Then, for all other images in the email, put them on the right-hand side of your email as most people use a preview pane which is the right third of their computer screen.
When I want to ensure my email reaches the most recipients I send it plain text - think typewriter.