It's hard to do. For one thing, you have to let the reader come to his own conclusions and not be told what to make of the events. Hmmmm. Lemme take a snippet and show you how I'd rewrite it (keep in mind that I'm a systems administrator by trade, and not a writer). Your quote:
She came over one morning a few days after I gave her the notebook. Rang my doorbell and awoke me from my nightly sleep. I stood and started for the door when I realized that it would be very improper to answer said door in my underwear. I returned to my bed, grabbed my blanket, and resumed my journey to the door. I made sure all of the proper bits of anatomy were where they were supposed to be, wrapped the blanket around and opened the door. "It's 12 o'clock and your still in bed?"
How
I'd rewrite it (first basic attempt with a couple of minor revisions):
The doorbell started me from a sound sleep. Springing from the bed, I stumbled to the door, nearly bringing several potted plants to the floor in my daze. As I was about to open the door, I felt the air conditioner kick on, and the realization struck me that I was still completely unclothed. I peered through the peephole -- Samantha.
As I walked back to the door, I made sure to right all of the plants so carelessy knocked down in my earlier pinball game of a stagger. I got the door open as the bell started to ring for the fifth time. She spun about suddenly, but stared for what seemed like minutes. Her car was blocking me in, the groceries in it trying to steam up the windows from the baking sun.
``Still asleep?''
What I
tried to do here, and I've obviously made up facts to fit it, is show what was going on rather than describe each event. I guess the first thing that I did was to make the events happen as the protagonist sees them. For example, the first thing that occurs to him in the morning is ``That's the doorbell!'', something I think we've all woken up to. Usually I wake up in a daze, but pretend to be awake by moving fast, and that usually leads to banging into doorframes and such. So showing that makes the reader identify more closely with the protagonist.
Also, instead of stating that it wouldn't be right to open the door nude, just show him changing. And you don't even need to show that, just imply it. We don't need to know which side he dresses on, either.
And the slightly silly reason he notices his unclad state just adds a slight air of verisimilitude.
Notice how he's in a daze before he realizes that it's Samantha, but afterwards he's righting plants, and it takes him another four rings of the doorbelll before he gets back to the door? Now, I don't know that that's accurate, but describes how his attitude has changed without simply saying ``Seeing that it was Samantha, he decides to answer the door after putting on some underwear, but it sure did wake him up.''
Also, note how he looked through the peephole before he decided that he was going to go back and put on some underwear? Does that mean he might have answered naked if it had been someone else? Does it mean that he might have just let the person go away? We don't know, but we know that it means something, and we know that it meant something to him.
Also, I never said that he put on nothing but underwear, but I implied it in the fact that he took his time, yet Samantha could still tell he had been sleeping. Also, the fact that it seemed like an eternity and that he started noticing obscure things like the groceries implies that maybe she was surprised about something, too. Maybe it was his attire. Maybe it was that the door opened at all. Yet she knew he was there -- his car was there.
And it's not early in the morning -- she's got groceries, and the sun is hot enough to be ``baking''. Also, they've been sitting in the car long enough for the store's refrigeration to be leeching from them. Has she been driving around for hours, thinking about stopping by?
Not to mention the use of more emotive verbs. In the first paragraph, I try to use sudden, lurching sounding verbs, to convey that just-woke-up-must-be-awake! feeling. But in the second paragraph, they become more muted, since his mental state has become that way.
See how much longer it takes to describe all of this than what was actually written? That sort of subtext is one of the potential hallmarks of interesting storytelling. It's not a necessary one, but I think it can be important very often.
And simply changing sentence structure around makes it feel less like work to get through. A constant barrage of subject-verb-object sentences is just a chore.
I suppose I could go on for a while, but I think that covers most of it. I'm sure that's not actually how it played out, but remember that you might want to make some stuff up that didn't actually happen in order to make it more interesting. Of course, if you want to be totally accurate, that's your choice, too. (And don't make fun of my writing -- it's just an example. You can do better.)
Edit: I want to point out that I don't want to influence your style. I'm just trying to give some examples of how you can show something without telling it. Also, I tried to cram a lot of different things into those few paragraphs. I don't think I'd suggest trying to keep that up. Writing can be too dense unless you're a master, and many of them can cut it dangerously close sometimes.
ReEdit: I think I remembered what that story put me in mind of. Harlan Ellison's Mefisto in Onyx. I think you might benefit from reading it. It's almost all internal dialogue, but it's very chilling and convincing. Very different from what you're writing, but somewhat similar in form. It might be hard to find, though. I think it might be included in the collection Slippage, but I don't know which version it is (it was rewritten between its publication in Omni and its book publication.