Take a look at the words first. The written words of "You are Beautiful" in Mandarin are: Nǐ hěn piào liang.
Start pronouncing. The pronunciation of the phrase phonetically sounds like this, "nee hey pee yeah lee un."
Divide the phrase into pieces. 1. Nee hey 2. pee yeah 3. lee un
Say it together now. Combine the phrases and speak faster so each phrase connects as one word.