Do not call her when she’s not awake or her fondness of Niko will go down.Also once you arrange a date with her do not take over an hour in the game’s time to pick her up or her fondness will also go down.However CJ's girlfriends, just like in real life, require upkeep and pampering, and the right care for their personality and tastes.There are six girls found around the map that are dateable.
Each girl will have her own taste and may not like the place you take her.
When the girl’s fondness increases she will invite you up for some “hot coffee” after a successful date and afterward your health will be restored to full.
The three internet girls will also offer an ability that you can call them up to use.
Consider flying your date in an airplane or helicopter if her location makes this feasible. They will be VERY appreciative, even if you are barely able to land (at least with the "Hot Coffee" mod which may have unlocked some additional uncensored materials). If you take Millie for a driving date in a helicopter she will quickly get upset about the speed and the date will end soon.
Do this after you complete the mission learning to fly.