Note that the following are my personal ideas about writing: they aren't professional any more than your own.
The first paragraph, until "I look around..." is dry. It is a simple summation of events, in the vein of, "Hello. My name is John, and I am twelve years old. I go to school at Arlington Middle School, and I enjoy a fancy walk in the Spring." It is a dull introduction which, the narrator not actually addressing the reader, should be omitted and replaced by sections that show the facts he's just summed up. You could, for example, attempt the following instead:
Whew. It really is nice to have a quiet evening every once in a while. It must've been last year since I've had my last quiet evening, and boy... that evening didn't end quietly in the least.
Now. Ashley's off to her friend's place for the night, so I've the house to myself, and there's nothing I need to do. Or can do.
You can apply the information about the parents and everything at a later point: you don't want your story to be an info dump that starts with information and then rattles everything off. Let people learn more about your protagonist as time goes on.
The passages after that stop being the narrator experiencing things: they are the narrator describing things that are happening as a disinterested third party. "A girl appears". "I just stand by and watch". "Her clothes are torn". "I'm unsure what I should do". "The first thing to cross my mind is that she's an Assassin". "The next thing I think is that her clothing's revealing".
The primary objective for a narrator is to narrate. However, the difference between an omniscient storyteller narrator and a first-person narrator is this:
The boy looked about himself. Here he was, in a room which, he was sure, was not his bedroom. He wasn't even sure it was a room: the surroundings were blacker than the darkest night, and aside from his own body, strangely illuminated, he couldn't see a thing.
"Hello?" he called out. "Is there anybody there?"
... Huh? Where... am I? I'm pretty much an expert when it comes to my own bedroom, and I can say with some certainty that this is not the bedroom I was looking for. No doubt my door, which had previously been just a bedroom door, has finally transformed itself into that magic portal to adventure I had always wanted... ten years ago.
Ten years, heaven. Ten years. And all you have to give me is this pitch-black room?!
In fact, is this even a room? I mean, what's with this pitch-black darkness, and why the hell am I giving off light?! I'm pretty sure whoever wrote the laws of physics and all would be rolling around in his grave if he'd see me here.
"Hello?" No response. "Anyone out there?"
To be precise, the first person narration gives the reader the unique opportunity to be party to the narrator's thoughts, rather than just a dry description of the narrator's actions. You have to ask yourself: who is the narrator addressing
? Is he relating a story what happened to him in the past to his best mate at the pub, over a glass of whiskey?
I was just sitting at home, you know. Ashley'd just gone off to that mate of hers. You know how she'd been right after pops and ma bought the farm, right? ... No, you dunce, I mean they died. Gosh, you're such an idiot.
Anyway, I was just sitting at home, drifting off in dreams a bit when suddenly SHAZAM! There was this brilliant light pouring into the room like... like... well, there's not quite anything like it in this world.
Ah, moment, lemme get a refill...
Where was I? Right, the brilliant light. I was staring at it all slack-faced, you can imagine, when out popped this girl. Not just any girl, but then, what girl does appear in a blinding flash of light? She had torn clothes all over and, well, I'd seen Terminator just a few days ago. For one wild instant I imagined she was some future assassin, out to prevent me from raising a rebel army. Hah!
Having a narrator begs the question, "To who is he narrating?" If he's experiencing things as they happen and the reader is to experience those things together with him
, you must let the reader experience all the wonder and awe your narrator is experiencing. It simply does not do for your narrator to stand there slack-jawed and in wild amazement, while dryly telling the reader, "I watch a girl appear from the light". Catch my drift?
You do this later on, but it's definitely possible to do it right from the start
. Additionally, lines as these:
"She seems to remember something before she speaks and stops, deciding not to say anything."
This makes me wonder: how does
someone look when they remember something, try to speak, then stop in a decision not to say anything? It's a rather precise assessment of someone's character and actions, which at the time should be turbulent and vague; not to mention, a girl with torn clothes just appeared out of nowhere. You might be more surprised than to just describe it. Try it this way:
She looks at me.
"Ah. I... uh... mmm..."
She falls quiet, tilting her head left and right a few times, like a child struggling to decide whether she'll have a chocolate bar or a slice of cake.
Really, the second part, post "transition" is really good, and I'd advise revising the first part to be conform to that. I started writing as I began reading, and by the time I realised you knew all this but didn't use it for the start, I felt I had written too much to just discard.