...As your editing skills improve you will learn what you like, and what doesn't work and slowly you will develop your own
workflow and style. Early on in your photographic development, look at what others do, and if you like it ask them how they did it. There are as many ways to edit a photo as their are to take it. There is not a 'perfect' editing
workflow that can be written down and given out. As for what to look for. I would say look for editing that doesn't look like it has been edited. For me subtle, natural editing is the best. I want people to look at what my photo is of..the subject..not look and go, WOW look at all that editing. Less is more!
As a guide to start out:
learn how to do levels adjustments
learn how to crop
learn how to increase/decrease contrast
learn how to convert to monochrome
learn how to clone (to remove that bit of rubbish from the beach etc)
Learn how to sharpen
learn how to selectively adjust saturation (but do not over-do it)
Learn how to vignette
These are in no particular order, but they will stand you in good stead for the basics of editing and you can achieve fairly much anything, if you can do the above, well.