If you want to compliment someone on their achievements, you can say:
(Che) Bravo! Good job!
Bravissimo! Excellent job!
If you want to compliment somebody in the specific circumstances of a wedding or graduation or a promotion at work, you can easily say:
You might want to add depending on the context:
Congratulazioni te lo sei meritato! Congratulations you deserved it!
Complimenti per il traguardo! Congratulations for the achievement!
If you want to make a physical appreciation, you can use the formula:
Che + adjective
Che bravo studente! Good student!
Che begli occhi! What a nice eyes!
Che bel bambino! What a beautiful kid!
If you want to make any kind appreciation, you can use the formula:
Come + verb
Come sei bella oggi! How beautiful you are today!
Come sei stato bravo oggi! How good you were today!
Come parli bene italiano! You speak Italian really well!
Come guidi bene! You drive really well!
If you want to compliment someone for their appearance or looking in a good shape:
Stai proprio bene! You look great!
Sei in forma! You are in good shape!
Ti vedo in grandissima forma! You are in a great shape!
If you want to make an appreciation of somebody’s look or style:
Il vestito ti sta benissimo! The dress fits you very well!
Questo taglio di capelli ti sta da Dio! This new haircut suits you very very well!
Ti sta bene questa gonna! This skirt suits you!