I want to do better at my job.

Hi everyone! I work at a local pizza restaurant as a guest service team member (busser, food runner and host) and cashier. I have been doing good at my job, but in the last 2 days, my managers on duty had a talk with me about my work performance and I have been though it before. It made a realize that slow days can be as pain as some of the busiest days. They told me that I need to start asking them and the shift managers if I need to get anything done more often but it's sometimes hard for me to do so since I'm introverted and struggle with communication skills. I need to help out and do whatever needs to get done more often instead of standing around whenever I don't have anything to do, but the problem is I cannot be in a work mode, instead, I easily get bored, zone out and daydream. Another thing, I do not get along with one of my co-workers and it's hard for me to be around her. What should I do to do better at my job?