Just prepare yourself mentally. Know that orgo is tough but if you come prepared for every class starting day 1 then you should be fine as Pagan mentioned above. I know that for me, I was really nervous my first day of orgo because of all the hype surrounding it so I made sure to hit the ground running by giving proper attention to each lecture starting from day 1. It helped me out immensely, I never really felt behind, and I REALLY came to enjoy orgo for the awesome subject that it is. Have fun
P.S. I also did genetics at the same time as orgo II. It's tough but definitely possible. Again, treat every lecture with priority and don't slack off.
I pre-read Organic Chemistry by Klein (the white TEXTBOOK) for organic 1. Doing so absolutely helped me. By the time i started class I had finished stereochemistry. Recieved an A and the highest grade.
I didn't pre-study organic and was able to make an A. It probably would have been a bit easier if I had pre-studied though.
If you wanted to pre-study, learn line-bond drawings, functional groups, nomenclature, boiling point trends, review acid-base chemistry, stereochemistry. I wouldn't worry about mechanisms until class starts.
Don't go too in-depth without obtaining a syllabus for your class. Khan Academy and Organic as a Second Language is helpful.
Agree with everyone above. Draw hexagons. But PLEASE do not actually pre study for these classes. There is really nothing to worry about. You hear all this bad stuff from other science majors about orgo being hard. I will be brutally honest. The students saying that are dumb, or not putting in the work to achieving good grades. Getting an A in orgo and genetics was not that difficult, and I think if you put in the work you will see good results. Good luck, and don't listen to other students.
Wiki premed has a neat little pocket guide of mechanisms along with accompanying videos.
I wish khan academy was more organized like it is now when I was in school. I wish I'd spent more time getting fluent in the big picture stuff that the MCAT focuses on in orgo instead of getting lost in the weeds with mechanisms.