Here some mathmatical apporaches to it, the rules of thumb apporach is at the bottem, if anyone knows any exact equations for L/D with tail winds and head winds, please post them, I can only find ones that are based on sink and thermals.
When it comes to weight and you want to find the best L/D (which happens at a spefic AoA) you can use this equations
V2 = V1 time the square root of(W2 over W1 )
This is where V2 is the speed that you want at weight W2
And V1 is the speed to keep that AoA with the weight W1
It works much better than using all those charts, they are often time consuming. This formula is proven out in most Aero. Engineering classes.
As far as and equation for Speed to Fly for L/D for head wings and tail winds couldn't find any in my soaring books (at least any that I could understand) but its has something to do with the tangent of the wind on a polar graph (thats about all I could gleam from it).
Thats the mathmatical apporach.
Rules of thumb:
Head wind = slower ground movement for every foot of altitude lost, so you would land shorter than the optimum distance.
Tail Wind = faster ground movement for every foot of altitude lost, more distance than usual L/D.
Heavy weight = faster flight at that angle of attack, so same L/D but you are doing it much faster (this is why a heavier gliders are better for flat out racing with no thermaling)
Lighter weight = slower flight for the same AoA, so same L/D, but you are going slower.