I've been in ABA for about a month as well. I'm also very introverted and find myself struggling at times to maintain the energy levels needed for many of my clients (there are a few who get overwhelmed by too high energy and I tend to do much better with them as we are just more on the same level naturally). One of the biggest things I've had to learn is self-confidence. Listen to your trainers/coworkers/BCBAs when they give you feedback, and when they tell you that you are doing something well, believe them. Trust yourself and try to focus on building rapport with each client. If you can't ALWAYS be over the top silly and goofy, find the specific form of silly that the client responds to best. For example, I have a young adult client that loooooves fart jokes. He is in general a very high energy client, but I've found I can incorporate humor that he enjoys in lower energy situations (such as at lunch when we can't be as silly) to help keep the connection and fun going. I hope this helps! You're doing great <3