This is in response to a request in another thread ;)
The 737 family has one wheel per landing gear and distinctive nose and tail:
The A320 family also has one wheel per landing gear with 'lower' nose than 737:
The 757 has two wheels per landing gear, the wheels lie parallel with the ground, the fuselage is long and thin:
The 767 has two wheels per landing gear, the wheels 'lean forward':
The A330 has two wheels per landing gear, the wheels 'lean back' like an A340:
Once you know which is which, it becomes second nature and you stop looking at the wheels and just recognise the fuselage shape.
Hope that helps :)