Make your elements appear more defined
Use Multiple Drop Shadows, or a very subtle border (just a shade darker than your actual shadow) around certain elements to make those elements appear a little sharper, more defined, and help avoid those muddy shadows.

Creating long-form content? Give 20pt, and up a try
#18pt is sooo last decade.#

Your shadows are coming from one light source right?

Improve Contrast between Text and Images with a subtle, but simple Overlay
Depending on where the text may be positioned over your image, you can either opt for a tried, and tested full image overlay, or a more subtle (bottom to top, or top to bottom) gradient overlay to achieve a simple contrast between the two elements.

Lighten up your text if it looks a little on the heavy side

The smaller the font size, the more generous the line height
As your font size decreases, increase the line height for better, all-round legibility.

Choose a Base Colour, and then use Tints & Shades to add uniformity

Always make your ‘Call to Action’ the most prominent item on the screen

Add an extra visual aid to your Form Errors
Adding an Error Message close to the action that the user has just taken can be a simple, but helpful, extra visual aid for when they’re filling out Forms of any kind.

Give Prominence to the most frequently used action in a Menu