Cant speak for everyone but I think they mainly want to confirm the following.
1) identifications and documents used in your application. Make sure you have all valid and original documents ready to present during the interview
2) physical presence days/exits in and out of the country. I suggest you go over your application again and refresh your physical presence calculator to ensure you can quickly remember each exit and entry
3) test your language proficiency through conversation. General topics like life, work and family.
In general, the immigration officers are friendly and accommodating. As frustrating as any immigration process can be, I cant imagine it is easy for them to process thousands of applications and all with varying cases. So be kind, respectful but don't be afraid to ask for clarification on things you might have doubts about or questions regarding your application. We all know it can challenging to get more information later. If you have an interview set up, don't stress too much about it. Refamiliarize yourself with the application you submitted and go for a refreshing walk before your interview
Goodluck