Then or than?
Although it's quite common for these two to be confused, it's one of those that is simple to resolve.
'Then' has to do with the passage of time, or with a sequence of events.
'Than' is a comparative conjunction, allowing one thing to be compared with another.
'Sarah went to see her mother, then travelled the short distance to see her brother, and then she went to the supermarket and met the man of her dreams over the cheese counter.'
'Sarah has more than one sister; in fact, she has three.'
'If you don't stop that, Bernard, then I'll slap your face.' (though, in fact, the 'then' in this sentence is redundant – try it without and you'll see there's no loss of meaning. But it illustrates the point, I think.)
'I'd rather you kissed me than slapped my face.'
Pic: Suspension bridge over the Humber Estuary.