[Many steps in the tip below are geared toward beginners as they learn about their images and their programs used to edit them. If you are familiar enough, being as meticulous can be skipped.]
If you have a series of photos to be edited, lets say there's a color defect, so your process to color correct is being repeated over and over again, you'll need to keep track of your actions. From your first image type up each and every step you take and settings you use. Some settings will save, some won't. Put these in a notepad document and save it with a title to match your project. Even if you make a mistake, don't erase the mistake you typed up, keep it (trust me, you might need this info later), just put on there that you hit undo until "this" step. The reason for this is if you undo, then move on, then realize you actually had it right the first time, your original steps are gone from the Gimp undo dialog. The only way to get that back is to back track through your document or if you saved your edited image before you hit undo.
Once you get your steps right for how you want to edit your series, save the original notepad document, then resave again under a new name. Alter the document to reflect only the steps you need to take and take those steps on your next image. Did it turn out the same? Note: certain items will need to be tweeked from one image to the next do to lighting changes, etc, however the basic steps and settings should be pretty close. You don't want to color correct a series and later see that one photo has too much blue taken out and another not enough. Repeating the same general steps will prevent this. In real life colors shift a bit and is so subtle we don't notice but in a framed collage setting someone will if you don't do it correctly. You could say this is a "learn from my mistake" tip.