LMNH,
Solid advice that applies to both to the VFR and IFR pilots.
To add for the VFR guys, always have a good awareness of where you are. When the cloud base starts lowering down, make sure your situational awareness is high. Being able to put a lat/long from your handheld to your WAC can be critical. Remember that everyone is going to be sharing the same airspace to stay visual. Having a good idea of where you are will save you heart ache later on, with reference to other aircraft and terrain.
Give your position to other aircraft reference to a distinct feature ie: an Airfield. I doubt many (especially the IFR drivers) will have a clue where BS swamp is, where as "ABC 15nm NW of Lake Evil, tracking east at 1000'" will have more meaning to everybody.
VFR drivers, have an idea of the approaches for the airfields you operate at. Some days the IFR drivers will be under the pump and will be giving positions reference an RNAV waypoint or " 2nm outbound in the NDB-A approach" etc etc with limited mental capacity to deal with other traffic.
Keep an eye on your fuel, don't miss a fuel drain in the wet season as the noise will soon stop if your tanks are full of water.
If you operate within phone and weather radar coverage, keep an eye on the weather as it passes through. Sometimes waiting on the ground for 30 minutes can make all the difference between dark and gloomy to reasonable.
Cheers.