Repairing a gas fireplace is a relatively easy task and you will want to properly maintain and repair the fireplace so that when the frigid winter cold begins to permeate your bones, you won't be without the beautiful warmth and glow of your gas fireplace.
The most common problem for a gas fireplace is that the pilot light frequently goes out. Before going to any great lengths to fix it, make sure that the draft spill switch is not open. If it is, reset it and also check to make sure that the vent cap shows no gaping that can be the source of a perpetual down draft. If that doesn't solve the problem, check the pilot light by lighting it and seeing how long it takes to go out. If it extinguishes quickly, then the problem is most likely a weak or malfunctioning thermopile generator. The normal life of this generator is four years so if you are near the end of the life cycle, call a repairman to replace it. If the generator is working well, then you may have to replace the main gas valve. It may not be opening properly. Try to clean it and see if it works and if that doesn't solve the problem, replace it with a new one.
If the pilot light is working and you are not getting a consistent flame, you need to check the main burner. You may be getting low voltage to the gas valve. This will cause slow starting and eventually no flame starting at all. Check your wiring to make sure that all of the connections are right, and secure any that are loose. And if you are noticing soot and other dirt and debris, your flame may be burning too rich a mixture. Adjust the shutter on the burner inlet to increase the air flow.