"With the season" just means "with the time of year", i.e. "with Christmas".
"To lay it" is a little trickier. To lay something can mean "to put it down", but an older meaning is "to put it away". The something, in this case, is "this Ghostly little book", so "to lay it" means either to put the book down, or to put it away. However, Dickens is having a little joke with his readers, since "to lay a ghost" means to exorcise it.
lay the ghost of sth (to rest)
to finally stop being worried or upset about something that has worried or upset you for a long time:
- With one stunning performance, he has laid to rest the ghost of all his defeats last season.