Don't call her too frequently or her respect for you will drop.
Dating gta 4 lost damned
Note that you cannot date a girl when you are on a mission.
After a date, you need to wait 5 hours (10 real-time minutes) before calling your girlfriend again.
Call your friend and perform activities with him on a regular basis to increase your 'like stat'.
This stat (amongst other friend stats) can be accessed from the pause menu under the 'Stats' section.
Don't take your friend to an activity that he doesn't like or your 'like stat' will reduce.