Hit Them With Their Weakness
When encountering a new shadow in Persona 5, your best tactic will be to hit them with every elemental attack you have. This will allow you to see their weakness, and it will register forever basically. From then on, you’ll be able to just hit R1 and quickly go to whatever will make them drop. Keep in mind that your gun can also be a weakness for some shadows, particularly ones that fly, I’ve found.
Making sure that everyone is dropped also holds a great strategy within Persona 5. When all enemies on a field have been dropped based on their weakness, you can enter a “Hold Up.” At this point, you can negotiate with them, or you can easily kick their butt with an All-Out Attack (triangle). This will be a really cool team attack that will wreck your opponents for a quick win.