Hi,
Resizing is certainly a helpful skill to have. But, you should know that there are as many ways to do it as there are software programs around, such as Photoshop and many others, that will let you do it. The concepts are the same in almost all of them, but the exact mouse clicks and key strokes will most likely differ. It’s also a skill that you most likely won’t be using every day, and it’s easily forgotten. What I’d suggest is that once you get it figured out for yourself, write it down someplace so that you don’t need to remember it. If you do it a lot, you’ll eventually remember it anyway.
It’s important that you talk with the person using the image in order to understand what they actually need. As mentioned, if you’re image is going to be on a website, 72 PPI is fine, and there’s really no advantage to going any higher. However, for printing, it’s not as clear, so just ask. Different printer manufacturers specify different “best” DPI values for using their printers, and even with that, some users of these printers find that they have success using other values depending on the image being printed, the type of paper, etc. Not all images can be resized “up”, ie, larger, without some extra steps to protect the quality of the image. There are more variables with printers than with web display, hence the need for discussion. If you are on a deadline, you “do what you gotta do”, but understand that you may not get the best representation of your art if you are manipulating the image. As with many things, “it depends”…….

Excellent post Alyson!

You can also set “actions” in Photoshop to automatically resize and save your images to whatever specifications you want, ultimately saving time. You can then batch process a folder full of images which really saves time. I currently have 2 actions. One is labeled “Web” and it resizes images for internet use and the other is labeled “Submissions” and it keeps the resolution of 300dpi but downsizes the actual image and saves as a JPG. This one is for art festival and gallery submissions. Of course I always double check the requirements just in case. Sometimes there are a few venues that have different image requirements than what I have programmed in my action. I keep my originals as TIFs because TIFs rule!

Is it really more agreeable to send high resolution images in JPG format rather than, say, tiff or PNG format because JPG files are smaller (bytewise, that is)? I keep my master image files in the format native to my graphics program (PhotoImpact8) because they are lossless and smaller than TIFF. I probably should convert them to something more universal (such as raster, perhaps?). I feel better having master images in some kind of RAW format. Jpeg is lossy meaning that every time you save it you lose some information which results in slow but additive degradation of the image.
I use 360 ppi for high resolution and 96 ppi for display (on a monitor). My monitor happens to be set for 96 rather than 72 (that tells you how old it is!).