My tip is about composition. In portraiture, if the subject is taller than it is wide, the appropriate framing is almost always vertical framing. On a standing child, or a seated child shown from head-to-waist, a TALL framing is almost always better than a horizontal framing, which shows the subject in the central part of the frame, and then has a lot of dead, empty space. Subject/Framing coordination is the mark of a skilled photographer.
Most self-taught shooters frame things horizontally, because that is what they "see" so often in the work of other untrained, unstudied shooters. This is a sore spot for many beginners who see nothing wrong with poor composition; poor composition dominates, just as ill-fitting clothes and cheap haircuts dominate American culture, but we ALL can recognize the beauty of a custom-tailored suit or dress, and we can easily see the difference between a Super Cuts $8 on-sale cut and the work done by a top-level hair stylist. It's the same with "portrait" compositions on portrait subjects who are shot in "landscape" mode.
The sooner you start to ask the question: tall? or wide? as the FIRST question you ask yourself, the sooner your work will start to resemble professional work. Not kidding.