>>488008909I used to play the french so I can give you some advice.
There are 4 big lines in the french, the advance, tarrasch, exchange, and Nc3.
>ExchangeSimplest to deal with and the most common reply online.
>TarraschThere are 2 main variations for black, Nf6 and c5. Nf6 is very dynamic (I used to play it myself) but the positions in some lines get complicated very fast, and you have to be ready to sack pieces. c5 is much simpler and a much easier way to equalize.
>Nc3Most critical variation of the french, not easy to deal with. Here there are 2 main choices, Bb4 (the Winawer) and Nf6 (Classical). They're both pretty playable, but I think the Winawer is more complex and demanding. Important to note that if you play Nf6 you need to prepare 2 subvariations, one against e5 and one against Bg5.
>AdvanceThis is a pretty common reply against the french, with most white players playing some type of Milner Barry Gambit. There are many different ways to play, but I think most courses nowadays recommend an early c4 and playing on the queenside.
In addition to these 4 I would recommend having some lines against the KIA. It's objectively not very threatening but if you play in the classic french way there's a chance you'll get smashed pretty fast.
Now there is also the option of playing the Rubinstein against Nc3 or Nd2. This cuts down on theory a lot and in return you're getting a solid position that's hard to play for a win.
I would recommend using the Mosalenko book "The even more flexible french" since that shows a lot of different french variations that black can play through model games.