First sentences should grab. They grab and hold. Obviously, the first sentence is only one sentence... but most of the time, that first sentence is the most important single sentence of the entire book.
Grappling in your readers, to hold them for the whole novel, is the key to success. I'm not claiming to be an expert... but what I'm saying, is what all successful authors would say.
The first sentence, holds all the power. If you are going to publish something traditionally, this sentence has hundred times more actually. The reason? Because publishers often only read the first sentence. If you first sentence is good enough, strong enough, powerful enough, (I had to add those extra definitions, good is an overused and underestimated word) then the publishers will look at your novel or short story, with a little more interest.
If you can make that publisher intrigued in seconds, if you can hook him in the first sentence, he will read more. Once he reads more, all you have to do is continue that process of adding to excitement. If you can make that publisher turn the page, then your only steps away from being published.
If you can make the publisher read an entire chapter you have nearly won a fight that took you through uncountable adventures with your characters. Of course, your work might not be accept, but don't be too sad. That was only one publisher, there are thousands of others.
But right now, I'm talking about that first sentence. (see, I already went down a rabbit-trail).
In a few powerful words, you need to make the read think. You need to make him/her really jump into the book. First, spend a quick (but powerful) word on what the reader should be looking at, then go on with your best line of drawing the reader in.
Now, I can't tell you what should be your first line, because, well, I don't know what your writing is. But I can tell you advice, unfortunately, my fingers are starting to get tired, so I'll put it in another part.