How do movie/TV rights to characters work?

Seeing a thread about whether Marvel could use Galactus got me wondering this. I get that if you were negotiating the rights for say the Fantastic Four you'd expect it to include all four main team members and probably things like Dr. Doom but are there packages of characters that say Marvel or DC simply give when leasing the rights to a certain franchise? Are the movie studios going to the companies with a list of characters the want included when they set up a franchise?

For example, did the creators of Arrow have to know in advance to ask for things like Huntress or Ra's when they initially requested the other characters? Would they approach DC everytime they wanted to use a character (or at least one not associated with Green Arrow)?

It depends upon the company. In terms of Arrow, though, the producers have talked about it many times. They say they usually plan out episodes, and either they'll approach DC and look for a known character to fill the role, or else DC will approach them with a suggestion. I'm sure with some big ones like Deathstroke and Ra's Ahl Ghul, they likely went in knowing which character they wanted, but it comes down to DC. Like with the upcoming appearance of Ray Palmer, the producers stated he was originally supposed to be Ted Kord, but DC had them change it to Ray because they already had plans for Ted. So in Arrow, they approach for characters, whether per season or by block of episodes, as they've also talked about how DC is now allowing them use of characters they never would have been allowed to use in the beginning of the series.

With Agents of SHIELD, the producers have said they were given a list of characters they could include by Marvel.