Above all, never think of a thunderstorm as "light" even though the radar shows echoes of light intensity.  Avoiding thunderstorms is the best policy.   Remember that vivid and frequent lightning indicates a severe activity in the thunderstorm and that any thunderstorm with tops 35000 ft or higher is severe.   Whenever possible:
a) don't land or take off when a thunderstorm is approaching.  The sudden wind shift of the gust front or low level turbulence could result in the loss of control;
b) don't attempt to fly under a thunderstorm even when you can see through to the other side.  Turbulence under the storm could be disastrous;
c) avoid any area where thunderstorms are covering 5/8 or more of that area;
d) avoid by at least 20 NM any thunderstorm identified as severe or giving intense radar returns.  This includes the anvil of a large cumulonimbus