WiSSSSO!
The way I remember is
WiND- Which way is wind blowing- if high enough remember there are more fields within gliding reach downwind than upwind!. Pick a field into wind!
Size- Look for the biggest first!
Slope- Landing uphill ok provided not too steep- land downhill and ya wont!
Surface. Short crop ok- land with furrows, Rape- forget it!
Stock- Avoid the cows!
Obstructions- Look for wires (or the poles at least!)