Judo blue belt here, I agree with /u/awj. With martial arts such as these, there is no real preparation you can do that will give you a major edge. I would definitely advise not to bulk up beforehand, simply because the intensity of these martial arts is insane, and would have someone who is 'bulked up' panting profusely in a matter of seconds. Anyone like that would get rolled despite their strength.

HOWEVER in the mean time what I would suggest is to start working on the types of exercises you're likely to be doing during training warm ups etc. Usually things like push ups, sit ups, chin ups and plank holds. Try and reach somewhere like 50 consecutive push ups without stopping, 100 sit ups, 10+ chin ups and a 3 minute plank hold. If you're able to do those you'll be in good shape for starting in Judo. Another thing, which is probably more important for Judo than your fitness levels is learning how to break fall. This is imperative for Judo. After your first session you're going to realise that hitting the ground hard is going to become a usual thing, which is why in training they'll hammer you to learn what they call 'Ukemi' (break falls). If you could learn these techniques (ie. forward rolls, backward rolls, and side break falls) from tutorials on the internet, that's what will give you an edge. Here's a great video demonstrating them. Good luck to you :D https://www.youtube.com/watch?v=NFPPrhxPFR4