There are many websites about raising bilingual children. Here is one site that provides a good list of tips:
Bilingualmonkeys.
Here is a Chinese website giving a great summary of the difficulty of Chinese language education for oversea Children of Chinese heritage: 海外華裔兒童中文教育的有效解決之道.
Specifically for us, we have used or attempted all means imaginable to us to achieve our goal, including:
1) We speak to them in Chinese all the time, except for occasional English words and phrases and have them speak almost strictly Chinese to us.
2) We have them spend 3-4 months a year (split to two trips) in Taiwan with their grandparents since they are one, till about 6, then about 2 months (one trip) annually afterwards. There, they attended preschool and public school. For a number of years, it did require 4 adult trips to send them back to Taiwan twice a year. For one of those trip, the whole family flies back together and my wife and I would return about 10 days later. Then, I would take one Thursday and Friday off a couple of months later, fly back to Taiwan, rest for a day, and then bring them back, with the whole trip concluded in three and half days. For their next trip, I will take two days off work again and drop them off with my parents in Taiwan. My parents would then bring them back for us. Yes, I did accumulated quite a few frequent flyer miles then.
2) We raised them on Chinese version of Disney, Dream Works, Pixar, and Japanese animation cartoons and movies.
3) They started listening to Chinese pop songs and watch Chinese music videos, well before they started to listen to English songs. 先入為主! We have fun listening to and singing Chinese karaoke as a family.
5) As my wife and I both work full time, taking hospital calls, and work some weekends, we needed a nanny for our daughters. Over the last 6 years, we had hired five Taiwanese au pairs and one Colombian au pair through AuPairCare and EurAuPair. The Taiwanese au pair spoke to the children only in Chinese and give them Chinese lessons five days a week. We hired the first au pair from Taiwan who signed up with AuPairCare. However, over the last year, we have not been able to find new Taiwanese au pair candidates who sign up with either company. There are a few au pairs now from China. FYI, the annual expense is ~ US $20K, plus room and board. That's for up to 45 hours of child care a week and up to 5.5 days a week, with various restriction, rules, and regulations from the US State Department. BTW, au pairs are live-in nannies and can only do light house work related to child care only. They are NOT maids and cooks. So, the au pair's main job is child care and we want them to concentrate their effort on talking to and playing with our young children in Chinese, not cook and clean.
6) We homeschooled our daughters for a year and half with two classes in Chinese (Chinese and math), from second half of third grade through fourth grade for Charlotte and second half of kindergarten through first grade for Georgia. We relied on our au pairs and another homeschool mother (Caucasian, taught ELA) to help us with our program. Homeschooling was an eye opener for us and is limited by one's resource and imagination. It was a great experience.
7) We purchased and brought back from Taiwan various Chinese educational materials, DVDs, tons of books (fiction and nonfiction), comics, novels, etc. I love going to the flagship Eslite 誠品 bookstore in Taipei, where they have a large children's section. When I was growing up, I had to read comics behind my dad's back. Now, I buy comics for them to read. Also, I would purchase and bring back materials ahead of their needs, since it is difficult to get them oversea on short notice.
8) We introduce various forms of Chinese language expression, such as jokes, riddles, poems, stand-up comedies such as 相聲, cartoons, TV shows, movies, songs, etc... This provides a more well-rounded exposure and experience and made learning Chinese more fun and relevant.
9) We tried our very best to have Charlotte (elder one) achieve and maintain relatively "excellent" Chinese as long as possible. She became fluent in Chinese before becoming fluent in English. The goal is for Charlotte's colloquial Chinese to be better than her English for the first 6-8 years, such that she continues to speak to Georgia, her younger sibling, in Chinese. I thought from the very beginning that once the children converse with each other in English early on, it is almost game over. So, it was paramount that Charlotte's Chinese is better than her English for a number of years.