Unless your Yuna is very weak, the easiest thing to do is to stick with the party that you start with. The first part of BFA is a mad rush to deal damage, so, employ the use of Auron's Zombie Attack and Yuna's Curaga to damage BFA. Zombie condition also prevents BFA from gaining his Overdrive as quickly as normal, and nullifies the Yu Pagoda healing effect (one will damage him and dispel Zombie, the other will heal and charge, but it's not nearly as painful as when there are two). Quick Hit with Tidus when necessary. Don't bother with the Yu Pagodas, unless your Aeon's Overdrive is hitting them.

During the second portion of the battle, BFA starts getting mean. His attacks now do Area-of-Effect damage, and can cause random petrification, and other undesirable ailments. This portion of the fight is simply a long defensive struggle to stay alive without losing ground. Use Aeons when necessary (to finish the battle), or to block the Overdrive. If Petrify hurts to much, try bringing Rikku and using Al Bhed Potions to heal for large amounts of HP, as well as dispelling some of the more undesirable ailments. If you have Attack Reels, that's all you'll need with Wakka for this fight, but I strongly recommend against it, due to its random nature, and the importance of Yuna, who is faster than Wakka and can heal.

Remember that "Talk" with Tidus works only twice, and does two things: Reduces any Overdrive amount down to zero, and causes BFA to lose a turn (not delay, lose). Alternatively, you can whip out some Trio of 9999s with Rikku, and do things the cheap way (using Mix, and a variety of reagents). After this battle, you cannot lose the game unless you hit the PS2. Remember, no sudden movements.