Formal:
* Premièrement: This is the most common and formal way to say "Firstly".
* En premier lieu: This translates directly to "in the first place".
* Tout d'abord: This means "first of all" and is slightly less formal than "premièrement".
Informal:
* D'abord: This is the most informal way to say "Firstly" and is often used in everyday conversation.
* Avant tout: This means "above all" and can be used when you want to emphasize the importance of the first point.
Example sentences:
* Premièrement, j'aimerais te remercier de ton aide. (Firstly, I would like to thank you for your help.)
* En premier lieu, il faut bien comprendre le problème. (In the first place, we need to understand the problem.)
* Tout d'abord, j'aimerais te parler de mon voyage. (First of all, I would like to tell you about my trip.)
* D'abord, il faut aller au marché. (Firstly, we need to go to the market.)
* Avant tout, il faut être honnête. (Above all, you need to be honest.)
The best way to choose the right translation for "Firstly" depends on the context and the level of formality you want to convey.