The space around objects is as important as the object itself, possibly more. Each element should be considered in relation to the blank space around it. No object should be too close or too far away from everything else. Very rarely should things be touching or extremely close together. It is important to give things space to breathe. Try to even out the space on all sides whenever possible.

Letterspacing / Kerning

Generally, the larger that the text is the more the letters need to be closer together, the smaller the text is, the farther apart the letters need to be from each other. Copy text, normally, should not have negative values.

Maximum Body Text Line Length

Anything that a user is reading on the screen should be no longer than 20 words. Increase the margins or make columns if you need to fill larger space.

Button and Link States

All clickable links and/or buttons should have rollovers and active states applied to them.

Input Field Sizes

All input fields should be sized generally relative to the information the user is going to fill out inside it. If there are multiple fields usually they should be the same width or half the width of the other fields.

Fake Content / Lorem Ipsum

If possible, try and create content by just typing something that you think might work rather than using generic stock texts. Even if the designer is technically wrong or inaccurate it will be closer to the end content, therefore more real and better for the design.

Finishing Touches / Details

Never stop working on a page until everything looks good. Always take a look at the whole page once you're done working on it. Is everything looking great? Ok, only then can you move on. If you notice something else that wasn't mentioned, or doesn't look good, please fix it.

As Few Font Styles as Possible

Try and use as few font styles as possible in the designs. Formatting is best when there is an easy to understand, consistent hierarchy of styles. The more a person adds the more confusing it is for the reader. It is ok to add new styles, but before you do, look at the existing styles and if there is one you can reuse. If there is one that is very similar to what you where thinking of creating, then go ahead and use it.

Simple is Better, Less is More

If the design isn't working well, more design wont make it better. Try simplifying things. It is easier to design with less because chaos can very easily ruin a good idea or design concept. Like the great Dieter Rams said "Good design is as little design as possible. Less, but better - because it concentrates on the essential aspects, and the products are not burdened with non-essentials. Back to purity, back to simplicity."