The rule of thirds
The rule of thirds is a guideline that allows you to easily create a pleasing composition for your photographs. Basically, the photo frame is divided in thirds: with 2 horizontal and 2 vertical lines, you divide the photo in 9 segments of equal size. It’s like a 3 by 3 tic-tac-toe grid that you overlay over the frame of the photo. The your DSLR or you camera app (like Open Camera app) can even have a setting that allows you to make such a grid visible. Using that grid, the advice is to place the most important elements of your photo over the lines and even better: at the intersection points. This places the important elements of your photo off center and balances the overall composition so that it is aesthetically pleasing.
There are many theories about what is aesthetically pleasing, but it’s such a broad topic that I won’t go into that. My view on this is as follows: if you place the main element of your photo right in the center, let’s say your model with your brand new shawl, you will create a photograph that is quite calming and soothing but also very static. Everything is centered; everything is in equilibrium and it will stay like that forever. This is the impression I implicitly get when looking at a subject in the center. This feeling is even stronger if the photo is square. This can be very pleasing but is not necessarily what you want to use all the time.
If you place your model on one of the vertical grid lines using the rule of thirds, you will automatically create a more dynamic photo. This is because the eye of the viewer will have to navigate over the photo to see all the elements. The trick is also not to put all the interesting elements on one side and leave the rest of the photo sort of empty. There has to be some balance otherwise the eye will not navigate over the photo. So you could place your model on the right vertical grid line of the photo and something else, less important, on the left vertical grid line, for example a dog, a small tree, or some flowers…
Try it for yourself: take your latest finished project and bring a friend or family member to model it. Take a picture with your model in the center. Then take a picture with your model on one of the lines of the 3 by 3 grid. Also place another element of interest on the other side to balance the photo. Take several photos with small adjustments (zoom in, zoom out, go a bit to the left or right, etc.).
I introduced a composition rule, but keep in mind that photography is just like knitting: there are no hard rules; there are only many many ways to reach your goal. Nothing is wrong, at most, there are some less aesthetically pleasing solutions. Aesthetic is highly subjective and is a matter of taste. So I’d say as a first step: experiment! And as a second step: draw conclusions for yourself. Just like you might have a favorite cast-on or bind-off, you’ll probably have a favorite way to compose your pictures, one that you like and keep coming back to.