Realistically, you need an instructor to help you with your form. That said, I will second all of the guys who have said yoga. I take BJJ and I still do yoga, because it's very good for your flexibility.
Other than that, just work on getting in shape. If you want to train for a BJJ competition, that's going to be pretty much impossible without an instructor, but the level of fitness in BJJ comes from working with the gi on, which is basically a huge, constricting training weight. If you practice rolls and mobility drills along with squats, pushups (lots of different variations of the pushup) and kettlebell work, you should be in pretty good shape.
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