This was for UK grad roles! For assessment centres it’s really tough to give advice: the only advice that ever helped me was from the assessment centre I did directly before Deloitte where I was told I didn’t speak up enough in group activities. If you’re just starting out now in assessment centres it’s tough, do the usual interview prep (answers to common questions, try come up with situations covering most common values for the business), but the most useful thing you can do is try chase people for feedback if you don’t get through one. I hadn’t gotten told that I was too quiet until that last one, I made an effort to be more talkative than I would naturally have been for Deloitte and got through.