Although we are always told to write the patient's story, some attendings/residents will crush you if you write down one of those rambling twisted tales. My suggestion is to listen to the patient and then piece together a brief & simplified medical description of what has been going on with that patient ... it needs to pull together everything the patient and collateral said in a neat leading package. Hit the high points of the diagnostic considerations that you are going to have in your assessment (setting up your problem list/DDx and assessment later on) and very briefly mention the rest.
The HPI winds up being your interpretation of what the patient presented with all the confusing parts, rabbit trails, confabulations, and disorganization set aside as brief footnotes unless those are part of your medical workup. Personally, I just listen to the patient and then write the thing if it's not too long. You do want to capture the essence what the patient said. You need to state what you know clearly from the history and briefly identify areas that may be unclear or conflicting. Indicate if the patient has difficulty recalling certain key facts or explaining him/herself clearly.
If I needed to write the H&P while I'm meeting with the patient (as when taking a long psych hx, for example), I would ask him/her some small-talk questions about food she likes or where he met his girlfriend or where the best place to buy a beach umbrella is while I'm furiously writing down a key piece of history. If the patient is comfortable, s/he might even just tell you some key facts that unlock the mystery of their illness. Before (or near the beginning of) the interview you might try to lay out the basic structure of your H&P document headings as you get started. By now you probably know long each section is going to be for a given patient. Then just "fill in the blanks" so to speak. You might start with open questions and then get very specific, perhaps even to the point of yes or no questions.
As the patient skips around, you skip around in your document to the relevant section ... she starts talking about how she and her boyfriend smoke this that or the other, and you are in Social Hx. He covers summary items, and now you restate those in a descriptive way near the top of the HPI, essentially telling the reader what is going on ("... and when I slipped cutting the hedge with my chainsaw, the blade came down and cut the top of my thumb off ..." becomes "On day of admission, patient was gardening with a chainsaw and accidentally severed the distal ~1 cm of his left thumb ..." "Your HPI might start with summary sentence or two that sets the stage for what the basic problem is and then you have a little section for each aspect of what's bothering the patient. This helps you remember to get the pertinent "story" details for each problem (diarrhea, depression, URI, etc.). Your attending might want the summary at the end rather than the beginning of the HPI, but at some point, you need to tell your reader the key facts for the 1st diagnosis. You really don't want to provide a transcript of what the patient said, but key quotes can be helpful & appropriate. You want to write sections with a chronology in mind, but if you are writing an original during the interview, you may not be able to preserve the chronology if the patient skips around and you are required to write your H&P as you take it.
You will learn how to write what your attending/residents want ... however, try to get it down as quickly as possible to maximize your grade. You might even want to practice by writing an H&P for a character in a movie or TV show (even a video game, for that matter). Being able to write a quick & accurate note or H&P without needing a wordprocessor to edit is a basic skill that we all need to learn as part of training. You aren't always going to have a computer to enter your record on. Each service and attending/resident has his or her peculiar requirements -- be sensitive to those.
