Impedance Matching for 915MHz

You need a balun

http://www.activefrance.com/Antennas/page3.html

If I have a 915MHz monopole antenna, how should I match it to 50ohms? Can we use L C matching network? How should I determine the value of L and C?

Check the impedance nature of monopole antenna around 915MHz. If you find that it is not matched to 50 ohm then based on the bandwidth you may match with simple L and or C or L section or PI section etc.
Smith chart can help you.