The Quora link another poster submitted is a good starting place.

* Steve Yegge's advice (often cited when people ask how to prepare for Google interviews): https://steve-yegge.blogspot.com/2008/03/get-that-job-at-goo...

* Buy "Cracking the Coding Interview" and go through as many problems in it. It also gives a good rundown of Algos, DS, Space & Time complexity.

* If you've never done a Google (or other big company) interview before, you could also consider looking on YouTube to see some example interviews (e.g. how people approach a problem, how they talk it out with the interviewer, etc.)

If you don't end up nailing the interview, it's really ok. You can try again in a year. :) There are people who've done 2 or 3 tries at interviews before they get in.