Hi, and welcome to this part of the forum! There are an ever growing number of trip report writers that frequent these boards so any questions you have I'm sure someone shall answer.
In regards to writing a trip report, there really isn't all that much to it, but there are a few basic things to consider first.
1) What sort of trips do you go on? This can really determine what style of writing you go for, as a much more relaxed story about a journey between two points is totally different to a hardcore bashing session on the London Underground. For me, on the longer legs of the journey, I pay attention to what goes on in the carriage around me, and anything I find funny or whatever, keep a mental note of it, as it's likely* to have the same effect on the audience.
*not always though, that's the risk!
b) Speaking of, who actually is your audience? Is your report aimed at the seasoned rail enthusiast or more of a layman's journey report? We bashers have a whole dictionary of terms that the average Joe wouldn't have a snowball's chance in hell of understanding! Consider that when writing the report.
3) Have fun writing! Seriously! Make the writing sound like you're enjoying writing the piece, and people will enjoy reading it. Think of it as a phone conversation; you can't see their reaction, you don't know what else they're doing at that time that's fighting for their attention, but you don't want them to hang up. Talk to the reader, make them feel welcome, include a joke or two to keep the piece light. Sure, you can list your moves and numbers with a bit of context to them if that's what you wish, but I always think it better to put a bit of personality into the writing. People on here like Techniquest, Kite159 & Fishquinn, to name but a humble few, have been writing these things for years so have a read of a few of theirs to get the picture, and just steal little bits that you liked from everyone's styles...that's how I started!
I hope this mindless rambling will help you somewhat and doesn't just confuse you more. I look forward to reading what you write!
Alex