Hi,
unfortunately I didn't pass any courses or guidance for preparation. But I've touched many materials as I actively searched for best materials to teach myself and from my own experience I can recommend you those that I've found the most rewarding.
As for the exam and specific self preparation itself I guess this manual is the e that can be found:
https://w w w.amazon.fr/TEF-250-activit%C3%A9s-Sylvie-Pons/dp/2090333480
Of course there some TEF test examples on Youtube. You will find more in the sidebar based on the context but here is something to start with:
https://w w w.youtube.com/watch?v=cIjyVp8XTQ4
Do not miss the version with corrections:
https://w w w.youtube.com/watch?v=JtBPsiBcP1o
Please note: usually such videos have their versions with corrections. The link is printed in the description of the original video.
At least you will get a good understanding of what the exam looks like and what are your chances to succeed in it.
As for the general preparation I can tell you that the most important factor is your perseverance on it. Still I can recommend these three books what I feel helped me the most:
https://w w w.amazon.com/Oxford-Hachette-French-Dictionary-Marie-Helene-Correard/dp/0198614225
This dictionary looks big and daunting at first but actually it has a very smart way of teaching you the word sense through the context of very apt phrases and in the context.
https://w w w.amazon.com/French-Grammar-Really-Teach-Yourself/dp/1444179438
Simply the best grammar for the beginner that I had in my arms.
https://w w w.amazon.com/French-English-Bilingual-Dictionary-Dictionaries/dp/1465459286
This one is great when you don't have enough time to study seriously, let say when you drink your coffee and take a snack.
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Sorry folks for a long reply but I find this more worthy and useful to occupy some space here than the never ending annoying "It's just 10 minutes after the ITA announcement, where the hell is the email?" or "My score is 489, do I stand a slight chance at the next draw?".