I got into a Quant Program this cycle and can share my experience and what I did.
1) read the quant program website for the program you’re applying to. When you come up with questions about the program, make sure they aren’t already answered on the website or the FAQ.
2) definitely review your previous research and be prepared to talk about the methods you used and why your experience led you to choose a quant program. What was the value you saw in pursuing a quant program vs any other psych sub-field.
3) continuing on the last one, be prepared to talk about why a quant program is right for you. I spoke a little about how training in quant methods would grant me more freedom to tackle complex research questions.
4) read your professors work! You don’t have to be an expert but you should be able to ask questions off the top of your head or seem conversational.
You don’t have to be an expert on the methods your professor is using (you are going to school to learn those after all!) but you should brush up on them and make sure you are not clueless.
More than wanting to learn specific methods I talked about why learning about quant methods in general is important to me and to the work I wanted to do down the line.
Those are the things I can come up with off the top of my head. Hope they help. Best of luck!!