1. ‘Though’ is always followed by ‘yet’ in a sentence and not by ‘but’.
Though he is rich but he is kind. (Incorrect)
Though he is rich, yet he is kind. (Correct)
2. ‘Not’ is never used with ‘unless’ as ‘unless’ expresses a condition that is always used in the negative sense.
Unless you do not pay the fine, you will not be excused. (Incorrect)
Unless you pay the fine, you will not be excused. (Correct)
3. ‘While’ implies a time duration of doing something and ‘When’ denotes a general sense.
When learning how to box, the technique is of utmost importance. (Incorrect)
While learning how to box, the technique is of utmost importance. (Correct)