Firstly, good private proxies are very important.
The next thing is a number of accounts per IP. I used to create about 5 accounts per IP, but now I create only one account (myself) per IP and got better results. By the way - avoid buying Youtube accounts. They're often massively created on the small amount of IPs.
The other very important thing is not to generate any fingerprints (to avoid multi-account ban). I mean for example: don't use the same unique phrases in video descriptions on many accounts (the same thing is about URL's in descriptions - it's worth using bit.ly or other URL-shortener).
Don't upload videos instantly after you created an account. Upload videos after at least 24 hours since creating an account.
Also, as peterbruce said, you won't be able to avoid to ban completely. It depends on your niche and competition.