Yes, you have to be good at programming to get into Google, but don't have to be perfect. But in my personal opinion, the most overlooked element is motivation. Interviewers want to see genuine motivation in you. This means that you have to show interest in technology outside the classroom, i.e. show that you're extracurricularly interested in software development. For me it was the website I made, travelfreedom.io, and every single interviewer asked me about it. And I passionately told them about it. So for me, I believe this was a good way to stand out.
To prepare for the interview, code in Google Docs, or any other text editor without syntax highlights or any help. In the interview you'll be asked to code in Java, Python, or whatever language you choose, in Google Docs. Doing that a lot different than writing programs with IDE, or even simple syntax highlighters. You will confuse brackets, indentation will be hard to maintain, and so on. Therefore you'll have trouble if you do not practice coding on text editor. Another thing is that know the language you choose very well - I've chosen Java since having SCJP and OCM certificates, I'd like to believe that I know Java well. However at some point during the interview I could not remember whether
.size() method. This however did not matter for the interview, which brings me to the next point.
Be ready to be caught off-guard. Everybody has a plan before they get punched the first time - Mike Tyson. I love this quote. Every time I'd try to spar someone in boxing, I'd have a plan in my head, yet once I was in the fight, my initial plan never worked, and I had to adapt. The same happened to me in the interview - many of the questions got me off-guard. Some questions I answered plain wrong. However I did not let that knock me off balance, and I kept answering questions to my best. Don't let the mistakes you make affect you. You will almost certainly not get the answer 100% right, and that's not what the interviewers are looking for (they want to see how you think, but you probably know it already from books like Cracking Code Interview).
Disclaimer: these are all my personal opinions based on my personal experience.