The most common way to say hello in Chinese is "你好 (nǐ hǎo)" - literally meaning "you good".
Other variations include:
1. 早上好 (zǎo shang hǎo) - Good morning
2. 下午好 (xià wǔ hǎo) - Good afternoon
3. 晚上好 (wǎn shang hǎo) - Good evening
4. 嗨 (hāi) - Casual "hi" (young people)
5. 吃了吗 (chī le ma) - Literally "Have you eaten?" (very common informal greeting)
Cultural note: In northern China like Beijing, people often use "吃了吗" as a casual greeting, similar to "How's it going?" rather than actually asking about meals.