It really depends on what you want to do with your French skills. I'm mostly interested in reading, so I started reading books (logically enough).
I'm not sure when exactly during this process I finished the Lingvist French course (as it was back then), but I started with short children's books, then read a detective novel by Simenon, and eventually read more complex and longer stuff.
Every finished book felt like a huge accomplishment! I didn't always understand every word or even every sentence, but I understood enough to follow the plot and to be able to judge if a particular sentence was important or not. And you can always go back in the book if you realize you've literally lost the plot.
I especially enjoyed reading books on the (free!) Kindle and Kobo apps on my phone, as they make it really easy to look up unknown words either in a French--English or French--French dictionary. And old books like those by Jules Verne are free to download! (You have to buy them, but the price is 0 €.)
On the other hand, managing to read real paper books feels like more of an accomplishment. And I felt that my reading ability was really improved by doing the Lingvist course. It was always fun to run into a word in a book that I'd already learned on Lingvist!
Oh, and of course I forgot: If you want to focus on your listening skills, I'd recommend finding a French podcast about a topic you are interested in. Not one for learners, but one for actual French speakers.
It will be really hard in the beginning, don't expect to understand that much, but hopefully your interest in the topic will help you keep going.
Thanks so much Annika! I actually studied French all the way to A-Level (last year of high school) so my french is quite good but over the years I start to lose a lot of my remembered words etc. What books do you recommend for someone who's intermediate at French?
I guess whatever tickles your fancy, really!
If the book is good and interesting to you personally, it will sustain your motivation when (or if) you have to work hard at every sentence and page. I usually find that the second half of a book goes much better than the first half, because I've immersed myself in the story, gotten used to the specific vocabulary used by the author, and already feel proud of how far I've come.
Reading something in French you've already read before in English is one idea. I know a lot of people have enjoyed reading Harry Potter in French despite being beginners/intermediate learners, because they already knew the story well. Some people frown on reading translations, but I think reading something you are familiar with trumps that kind of purism. Any reading practice helps!
So whatever you enjoy and can get hold of in French, basically.