I think the subject is different depending on simply how musical you are naturally. Music theory kind of explains why some things work, while others don't - and much of this is genre irrelevant. Trance isn't something I'm remotely into - so I looked on youtube and found this one
YouTube
Now trying to look at music theory - you have the obvious time signature stuff. 4/4 seems the standard one, tempo range is also something to be able to understand, but that's the simple stuff. Chords in that example are pretty much the same as other music - but those examples seem to favour minor chords - more than I'd have guessed. One of them also had m7ths and even suspended 4th so to understand the song construction in just overall music styles, you'd need to have a look at chord construction - key signatures with their different sharps and flats, in the circle of 5ths layout - and oddly the format of the chord changes could even be looked at in the Roman numeral system - I, IV, II, VI, V etc - as the actual key of the songs is perhaps not that important - they key perhaps being set by a particular sound that sounds great on one particular note, and then you build around it - and if the key sig happens to be B major with loads of accidentals, so what? You could also look at the chord progressions, as in why does the next one really work, and what the relationship with the previous one was. Trance also appears, from that tiny sample, to not really have a melody, but little riff type sequences that also seem to follow the notes in the chord. The bass end seems to be mainly the root note and octaves with some Perfect 5ths - as is quite normal, but lots of non-trance features of chord progression based music are ignored. One chord songs are far more common - but things come and go to give texture and change, rather than a new chord. Structure is also different from the usual gluing together of c hunks of the complete song - in the Verse, verse, chorus, verse type construction. You could count the bars that make up each chunk and see if they fit the usual 12 or 16 bar conventions.
Pretty much you'd be exploring a huge subject and seeing which bits are relevant and which bits aren't - but it would explain why some thing won't work - so you'd be learning the rules to a massive range of styles and then seeing how yours follows the rules - or possibly breaks them. You might discover that learning the theory could help give you ideas, or maybe just make writing the stuff easier, as you'd soon recognise the way they help. There are loads of those trancey sounds on one of my synths, with drums and weird snoopy noises - and I do play with these sometimes live in the studio, and Music Theory will help you pick where to go next - so if it's making great noises playing Am, then I might take the Am, C and E, and raise the E to an F, turning it into an F chord, or going from the Am, C and E to Am, C, D and F making a Dm7 - music theory would help you understand why these chords might work, while others might not. It also helps identify wrong information.
When I was a kid, experimenting with my first keyboard my aged granny said that you never play two white notes immediately next to each other - like B and C or E and F, and a few years later discovered that of course you can if that sound works for the piece - She was thinking about music with basic chords - my favourite chord is the Major 7th - which my granny would have hated.
Some of the very strict stuff - like parallel 5ths, and the rules on that kind of thing might not really be needed, but some of the stuff like figured bass was really produced so performers could do their own thing with bass lines rather than reading them and playing them the same each time - pretty neat for people hundreds of years ago. If Bach had had a synth - I reckon he'd have found it amazing in the textures and blends of sound. In history - every time a new instrument was invented - the popular composers wrote for them, using the new features. ~Music theory has been a kind of constant rule book to follow that works.
Trouble is - it's hard to understand and only vaguely important if you're already good at making your kind off music. You probably are following the rules already because you discovered them for yourself! You could find some though, that explain why some things DON'T work!
