A novel’s first sentence should indeed be an opening line, a doorway into the rest of the book. Ideally it should be such an inviting portal that the reader can barely resist entering, which means it’s a tricky task for most authors. There are many famous opening sentences but here’s my favourite:
The goats were poor traveling companions.
This is how David Dodge opens his man (and woman) on the run thriller The Lights of Skaro, first published in 1954 and long out of print (I think). Dodge is better known for his previous novel, To Catch a Thief, made into the famous Alfred Hitchcock film, but in my view Skaro is a substantially better book. In fact it’s one of the best man-on-the-runs I’ve read. Seek out a secondhand copy and I don’t think you’ll be disappointed.
And who could resist an opening line like that?