Marbling is the art of printing multi-colored swirled or stone-like patterns. It is usually used on paper or fabric, but the technique can be applied to other things like beauty or food. Here are some marbling photos:
These are a few image editing and Photoshop tips I've learned.
This Fresh Rag graphic explains what size your photo should be in pixels if you want it to be high definition. To make an image good quality, it helps to start with the image really big. This is good to know if you're designing graphics or want a really high definition image.
This image from Her New Leaf shows you how to save images correctly. If your image is a photo, save as JPG format. If your image is a graphic or just words, save as a GIF (like my Etsy logo). If it's a combination of text/graphic and photograph, PNG is the best way to save. This will make your photos look better on the web and more high definition.
Another tip I have with Photoshop is to save the PSD version of an image if you're making a complex graphic and have a lot of layers. That way if you need to edit it (like if you need to change text), you can easily find the layer you need to edit and fix it.