There's no such thing as "oh, today was just a bad day"
Your day, good or bad, is dependent on you
So don't be a dumbass and do things to make it a bad day
So how do we do that?
First things first, to make sure I have a good day, and perform good, we need to make sure our diet is in check, typically I wouldn't eat a full on meal around 3 hours before, so I train around 6:30, so I don't have a big meal anywhere around after 3PM, The only food I have is some carbs, maybe like oats or some fruit, or rice, around an hour before training, which is fine, as long as it's not too much of course.
And speaking of, don't train hypertrophy around maybe 3-4 hours before class as well.
Another thing I do, is a meditation before class, and just sit and focus on y breath, or thoughts about Jiu-jitsu, to get into the mood. That's something that's helped me a lot, so I highly recommend it. Maybe think of ways to submit someone, or take them down, imagine yourself doing something at BJJ, and having a good day, it's been shown that visualizations can help with trying do do something, if you visualize your self doing a flip, in very good detail, you'll be more likely to do it.
Look up Psycho Cybernetics, it's a book you can read that talks all about this.
One last thing, make sure you're getting good sleep, at least 7 hours, to 9 hours of high quality sleep each night. To make sure you get good sleep, sleep in a cold dark room, not looking at any lights around an hour before bed, staying away form screens, and tech in general.
Hope this helped, comment W if this post was VALUE!!!