Be sincere. Any compliment you say, you have to absolutely mean. Girls will always be able to tell if you don’t mean it. They may not call you on it, but they’ll know and it will make them feel awful and awkward.
Be respectful. This is the main key to being able to Compliment girls without offending or upsetting them. If you respect them as people, as valuable human beings with worthwhile opinions, feelings, hopes and dreams, who are capable of doing everything that you can do, then any compliment that comes out of your mouth will probably be fine.
Think about how the Compliment would make you feel. If you’re still worried, think about how the compliment would make you feel. Don’t just look at the surface of the compliment...think about the things that she worries about and the experiences she’s had. Think about what the compliment could mean if taken out of context. Think about how you would feel if someone you didn’t know said that to you. If it would make you feel uncomfortable, it’ll probably make her uncomfortable too.
Compliment at appropriate times. You need to compliment her at appropriate times, like when you’re on a date, or you’re having a conversation related to what you want to Compliment her on. This also means pairing what you want to compliment her on with the situation that you’re in. This is very important, as doing this in the wrong situation can be very demeaning.
For example, don’t compliment her on her physical appearance after she’s just given a presentation (unless it’s to say that she looked fierce and was commanding the whole room). Instead compliment her on her hard work, her great way of phrasing the information, or her clear intelligence shown in how she put the presentation together. Complimenting her physical appearance in this situation would be demeaning, but complimenting her work is empowering.
Show your compliment in your actions. You don’t always have to say a compliment for it to come across loud and clear. A very effective way to compliment her can be to show your compliment in how you react to something that she’s done or said.
For example, if she’s just worked very hard on something, you can compliment her hard work by treating her to a relaxing back massage.
Another example would be that if she does something really nice for someone, do something really nice for her, like making her dinner.
These actions can also be ways to introduce a spoken compliment, by telling her why you’re doing what you’re doing.
Accept rejection respectfully. If she doesn’t respond to your compliment in the way that you’d like, don’t be a jerk or think (or tell her!) that she’s stuck up or thinks too highly of herself. This only proves to her that you were complimenting her for your own sake rather than hers. Instead, tell her calmly that she doesn’t have to believe you but that you meant it sincerely and you hope she takes it for what it is. Leave her alone after that.
This is most common when complimenting girls you don’t know. Girls you do know will probably modestly reject a compliment because they are frequently conditioned to do so, at which point you can simply emphasize that you really mean it or think it, or just straight-up tell her not to be so modest.