Practice saying the words in front of a mirror. This might feel silly, but it works. You'll be able to see your own expressions as you say the words. You can fine tune your facial expressions and body language until you get it right.
Adjust your tone. Communicating feelings and giving compliments do not come easy to many people--so don't feel bad if you need to practice your tone to make it sound real, rather than sounding as if you are reading some line from a script.
Pick an appropriate time to speak. If she is talking about something that is bothering her, don't interrupt her just to say she is beautiful--it might simply come across as an interruption--as if you aren't caring enough to listen to her--rather than a real compliment. Wait until a more appropriate time if this is the case.
Look her in the eyes when you say these words. If this woman is someone you are dating or otherwise close to, it can help to touch her shoulder or even her hair as you say, "you are beautiful." Avoid any kind of touching, however, if this woman is someone you aren't in a romantic relationship with yet--touching might feel intrusive.
Allow her to take things from there. She might blush, frown, laugh or have some other reaction--that is her choice and don't push her for the reaction you want. A genuine compliment, like any gift from the heart, is given without expectation of something in return.
- If saying "you are beautiful" seems too generic, try complimenting her on specific qualities. Compliment her personality, her hair, her clothes or her voice, for example.
- A woman might react differently to compliments than you expect. True flattery and compliments are usually welcome--however, she may have experienced too many fake compliments from people who only wanted to manipulate her. Try not to take it personally.