Formal:
* Passer un agréable moment: This is the most common and formal way to say "have a good time."
* S'amuser: This translates literally to "have fun," which is less formal than "pass a good time" but still appropriate in many situations.
Informal:
* Bien s'amuser: This is a more informal way to say "have a good time," and is often used with friends and family.
* S'éclater: This is a very informal and colloquial way to say "have a blast," and is often used with friends.
Other options:
* Passer un bon moment: This is a less formal way to say "have a good time," and can be used in many situations.
* Profiter de (something): This means "enjoy (something)," and can be used to express having a good time doing something specific.
Examples:
* J'espère que vous passerez un agréable moment à la fête. (I hope you have a good time at the party.)
* Je suis sûr que tu vas bien t'amuser. (I'm sure you'll have fun.)
* On s'est bien amusés au concert. (We had a good time at the concert.)
* J'ai profité de mon voyage à Paris. (I enjoyed my trip to Paris.)
The best way to choose the right phrase depends on the specific context and your relationship with the person you are talking to.