I thought this was going to be another Reggie S. Potter thread.
they say that you never see the one that gets you, which is totaly logical, because if you saw him, you'd take avoiding action.
Practicing your aircraft spotting ouch, its that word) skills on the ground helps when you are in the air. If you heard an aircraft, look for it and watch how it looks against cloud or sky. Do the same with soaring birds and you will become more used to focussing into the distance.
Coming back with Mrs K on saturday, she saw at least one aircraft that I couldn't get on to, but rather than waste time looking for it, I told her to keep an eye on it & let me know what it was doing. I've got her trained not to worry about B747s climbing up out of Stansted now.