My experience with this, is if you compliment them on something they have control over, that makes a bigger impact. Whether it is their looks, or something they have done, look at what they had a choice over, and compliment on their choice.
For example, if where to compliment a woman on their choice of shoes, their sense of style, or something new they did with their hair, then that would have more impact than saying “you’re beautiful”.
If you know they made a conscious choice to do something, then compliment them on that specific thing. Saying, “I admire the guts it took to confront that person, well done”, is a lot more inspiring that saying “you are inspiring, I could never have done that.”.
My wife loves to cook. I could say, “I love your cooking”, and she would appreciate it. But if I was to be specific and say “What is that extra spice you added? That lingering flavour is sooo good”, she would beam.
Even saying I love you. If you want your partner to feel extra special. Be specific and tell them what you love in particularly about them.
And compliment on things you know are important to them. For example, my wife adores our dogs, and takes pride in their training. I compliment her on it all the time (our dogs are freaking better trained them me!). Particularly if I noticed little things she had incorporated into their training. If I can see improvements, or things I can see working, I compliment her on that choice all the time.
Oh, and lastly, mean the compliments. Woman can smell BS a mile away.