For character meals, bring your flash and shoot just like you would at home. For meet & greets around the parks, they are a bit harder depending on where the character is located. I carried my flash and diffuser around with me in my backpack and used it a lot, especially for the indoor m&g's. The outside ones, not as much unless the character was under some sort of cover or under trees like Peter Pan at MK, White Rabbit at MK, King Louie & Baloo at AK, Darth Vader at DHS.
For the others that were out in the open it was just a matter of adjusting for the time of day, sunny (is the sun behind you, behind them, etc...) or cloudy.
One of the hardest one's I had was Gaston. It was later in the day and half of his m&g area was shaded. That really messed up the sensor. Also Phineas & Ferb at DHS were in really bright sun and next door, Lightning & Mater were under a roof, but it was later in the day and very sunny so most of Mater was sunny and all of Lightning was in the shadows. Another tough one. I used a flash there to help with shadows.