I agree that lots of water is a good idea to keep away bloating. My brother used to take quite a high dose of predisone for his asthma and had a lot of bloating. I'd avoid too many salty foods and try to not eat too many frozen or canned dishes, as those also may contain more salt than fresh foods.
I notice that some people will eat more when taking prednisone, so just keep an eye out on your eating habits. It's common for some medications to cause hunger and increased appetite. My dog actually is on prednisone for skin allergies (small dosage for a pet of course), and we notice him having a higher appetite. We just keep his portions the same and give him plenty of water (he drinks more water too) and he is doing fine. Our vet said to make sure to give plenty of water and watch the food portions or he will gain weight, so it's pretty similar to what happens with humans.