Third part of Photoshop ethical rules. You should follow them if you want to have well organized workflow.
Please use effects and filters in moderation. PSD inheritors will have less to sort through, and in most cases, more filters ≠ better design.
It’s much easier to navigate the layer panel with color thumbnails that represent the color of the elements on the canvas.
A slightly-off repeating image is incredibly noticeable. It’s worth the time to get it right.
Without knowing how an image translates to CSS, you could be greatly limiting its use by loading it up with effects.
Gradients are meant to be smooth, and like everything else, it’s better to get it right the first time.
Using outside strokes when you really meant to use inside strokes could affect the overall width of a shape.
Not that any of the following guidelines will automagically make you a better designer, but they'll help your approach to working in Photoshop for certain. Just five of the many considerations you can be making.
Grids help guide (pun intended). Establishing a system of heights, widths and alignment for your design is essential.
Drop shadows, like other effects, need to be altered from the Photoshop default settings in order to look realistic or sophisticated.
Besides the amazing selection to choose from, webfonts are the norm. Not the norm? Text as images.
It’s best to design with the mindset of how things will adapt to different widths, as opposed to hoping everything plays nice after the fact.
Google Images is *NOT* a resource for stock photography. Examine use agreements before using icons and the like.