One element that, in my opinion, leads to both a successful portrait and landscape, is getting the entire subject in the frame. Whether the subject is the whole of something or a piece of something, the subject must be in the frame in entirety.
Had I gotten this with a grayish-blue sky, it would have changed the mood of the image that is achieved with the color. Had the cloud lines been higher, accenting the sky above the windmills, it also would have changed the scene (though I can only credit weather for working out that part of the photo for me.) The hills are curved lines, which harmonize the straight lines in the clouds............. (click read more)
Cropping at the elbows or knees can make people look like amputees! So the easiest way, naturally, to make someone look like a whole, real person, is to do a full-length portrait. However, lighting is also important. So is time of day (if you're doing an on-site portrait.) Lines are also very important. You don't want anything in the background bisecting your subject awkwardly (like through the neck, or out of the top of the head, etc.) The image below is a relatively-simple full length portrait ("Snowshoe Man" - Taken on Wolf Creek Pass, Colorado in 2008):
So do landscape photographers crop or move in close to subjects? Do they use implied lines? I follow some other landscape photographers, who most-certainly do utilize the details of an image. Sometimes the sky inhibits the shot, so they don't have sky in the photo. When shooting with Jay and Varina Patel, two such photographers, Jay said, "If there are distractions in your shot, zoom in and focus on the details." The image below ("The Great Sphinx at Giza" taken in Giza, Egypt in 2012) is by far my most-popular landscape photograph of all time and has been on two magazines, sold as prints, and gone wild all over the Internet. But you can't see the whole image. It utilizes implied lines! I zoomed in and focused on the details.
Some have said before that I shot this image like a portrait photographer! (Ok so? And what does that even mean?) I also throw like a girl, by the way. How would a landscape photographer have approached this image? Based on some work I've seen by some, I'd say they may compose it similarly if they had the same things to deal with as distractions in the foreground.
The same fundamental of zooming in and focusing on the details comes in to play with portraits, and it is equally important to make sure that lines bisect at natural places (I bet you never thought you'd use geometry in real life, did you?) and that the crop leaves an accurate implication as to where the lines continue. The image below ("The Joker") was taken in a place with lots of distractions, so it was essential to zoom in and capture the subject as a head shot.