When choosing crystals the most important thing is your intent as energy always follows thought. This means that before you even decide to choose a crystal you already have in mind what it is you want it for. Then see which crystal or crystals attract your attention. We are all different, each of us with different dominant senses, and there is no 'correct' way to choose once you have your intent in mind. Some crystals may instantly just stand out visually to one person, whereas someone else may 'know' without even looking. For someone else, a crystal gives off a 'tingle' or charge when they wave their hand over it. Other people may hear the notes of crystals or their senses of smell and taste may come into play.
Something that can get in the way with choosing crystals is choosing something because you've read it in a book that there is a 'right' crystal for whatever issue. Unfortunately I've found this can actually get in the way of choosing an appropriate crystal, and can hinder our intuition rather than helping it. This is because for any issue it always depends on what the original cause is in the first place, rather than the issue itself. For example, crystals do not work on a like for like basis with physical symptoms because a physical symptom is only an expression of something that is happening energetically at a finer level. Crystals, which are a form of subtle energy medicine, work on the original energetic cause of something rather than the manifested 'symptom'.
Of course there can be many different reasons why we would choose crystals, from the trivial, such as helping us to find a parking space, to the profound, choosing one to help us with our development as human beings or for within a crystal healing session. When a healer chooses crystals for healing purposes, this is very different, and this takes a period of learning and training, so the healer can choose using a combination of their intuition, experience and knowledge.
May you all choose well and wisely just exactly what you need!