Funny you mention, I just got back from Atlantic City dodging some level 4-5 stuff in a C172. Know the weather and weather systems affecting your flight starting hours before your departure. Call and get outlook, standard, and then abbreviated wx briefings. The charts on adds.aviationweather.noaa.gov and also on duats, and whatever your airport may have are invaluable.
The thing that made the biggest difference for me today was calling flight watch (122.0) just as I was leveling off, to get a final update on where the weather was. I opted to fly an alternate route once I got this enroute briefing that took me about 30 miles west of the original route, which was getting beat by some level 4/5 cells that moved faster than anyone forcast. I would have wondered right into that mess if the "flight watcher" hadn't have suggested otherwise, since my last look at the weather computer right before I took off indicated relatively clear skies along my route. Sometime you have to call 2 or 3 times before they come back to you, but I don't think we "little guys" have a better resource for enroute weather information than flight watch.
Also, I get flight following wherever I go, especially during the summer. Most of the controllers now have radar overlays on their scopes, and know that I have nothing on board! The controller today in Baltimore was awesome - she kept me updated with pilot reports for other aircraft coming from where I was headed. Generally if you ask for vectors around the weather they can accomodate. If you have a gps, let them know and they will utilize your ability to go direct, which also cuts down on their workload.
My CFI told me to never fly into a T-storm

which is pretty good advice I'd say; but at the same time, if they're isolated and widely scattered cells surrounded by clear VFR weather, its no reason to cancel a flight - as long as you are confident in utilizing the avoidence resources that are available.