Seating arrangement came in ASO 2012 (circular table, two questions). Linear rows and circular tables of 5 to 6 people are the usual forms. Place the fixed clues first, then the relative ones.
Linear row facing North
Your left is the viewer's left. "Immediately left of" means the next seat on the left. "Exactly one person between" means the two are two seats apart.
Circular table facing the centre
- Your right is the seat anticlockwise from you, and your left is the seat clockwise.
- With 6 seats, "opposite" means 3 seats away. The angle between neighbouring seats at the centre is 60°.
Method
- Start with the clue that fixes someone's seat (an end seat, or an opposite pair).
- Add the "immediately" clues next, then the "one between" clues.
- If two arrangements are still possible, test each against the clues you have not used yet.
ASO 2012: A is two places right of B, B is opposite C, C is immediately left of D, and D is opposite E. Clockwise this gives A, E, B, F, D, C, so E is between A and B, and the angle between C and F is 120°.