Google was by far the best interview experience I have ever had. They will provide you with extensive information about every step, so you will know how to prepare.
I applied via a referral of employees (you can just ask employees on LinkedIn) and many are happy to be your referrals. Then I had a short video screening call with the recruiter, a phone mock-sales interview and 3 in-person, on-site interviews.
How I prepared.
1. I went to 15+ company interviews, just to practice being in the interview mode and in uncomfortable situations
2. Digital Garage course on Digital Marketing from Google
3. Google Ads course from udemy (from guy with the hat)
4. Made a spreadsheet with all the questions I could find from glassdoor and quora (few hundreds). Split them into categories (behavioural/etc)
5. Practised the mock pitch with friends and implemented feedback. Reccomend for all the questions.
6. Read the book about Google (very good read too)
7. Contacted 10+ employees from Google and got information about the position, the daily work, etc
8. Hired a Google Interview coach and had 8 sessions (that helped a LOT). Just google him (g-hire coach)
The on-sites interviews were easier than that with my coach.
I maybe over-prepared but I really wanted this job.