I think it's always helpful to study the masters...study their shadowing and try to replicate what you love about it. The whole purpose to shadowing is to create REALISM, so I think the ultimate master is studying the shadows on a real, physical page...like from a paper scrapbooking gallery.
Let me link you up to some amazing paper galleries where you can just soak in the natural shading and shadowing taking place in the beautifully clustered and layered masterpieces:
Note that the shadows fall in a different direction depending on the photographers's light source. 2dogs obviously has a window or light source to the left of her page, Karola to the right, and Gabrelle's is mostly from the top. Notice how the shadows don't just hit the background, but they play off the other elements on the page as well. Look at the last example--the flower to the bottom left not only has a drop shadow, but there is also an obvious shading taking place on the flower itself from the petals that curl up to the right, blocking some of the sunlight. Notice where the shadows are tiny and where they are bigger, and especially notice that soft lighting gives soft shadows.
Speaking of soft shadows...lighten up! I mean...lighten up your shadows. Shadows that are too dark make your elements look stiff and stagnant. Lightening them up will create a more fluid, graceful feel to them. Example:
This page (above) uses the default shadow. It's a black shadow using a multiply blend mode--which looks awful on this light background paper. Plus, they are all the exact same size and distance from the background--no allowance for real depth. But you say, Krystal, I'd never use the default shadow. I change my depth. So here's another page (below) with the default color and blend setting, but with me changing my distance and/or size.
Improvement? Not so much. That much depth on those stitches looks absolutely ridiculous! And the deeper shadows look even darker and more out of place than the previous example. The key here is to lighten them up and give each element its own depth as appropriate. Oh...and use Linear Burn instead of Multiply. The result is much prettier.
See? BTW, this is one of the pages in my QuickPage set available here.
Here are some links to some tutorials to help you in your pursuit of Shadow Happiness. :)
And before you go, I'd thought I'd share some of my own shadow styles with you. These are not going to work for you 100% of the time...you'll still need to adjust opacity, distance, size, etc. for the perfect shadow, but you can use them as a good starting place. I created these in Photoshop CS3, and they should be compatible with most PSE versions, but no promises. :)
One of the things that I love adding to my shadows is an Outer Glow...with similar color as the drop shadows above, set to linear burn. I adjust the size and opacity to create realism and usually have to decrease the opacity of the drop shadow to compensate for this extra layer style. Here's an example where most things have an Outer Glow added
"Cornucopia" by Microferk Designs