When composing psy-trance music, having a modern or oldschool style depending on several factors like your musical approach, your own taste and your mood. It can be quite subjective nowadays, as producers tends to make a fusion between the two worlds. The way you are using hardwares and softwares instruments, the different type of synthesis for sound-design, the audio process and also your musical arrangement and structure of your production can describe your sound signature as "oldschool", as "modern", or both. Sometimes, the frontier between oldschool and modern psy-trance is very small. In fact, you can be inspired and influenced by each of them to create a nice fusion. Basically, the difference between oldschool and modern will be only the way you construct your music.
In the oldschool approach, a typical arrangement will be: an intro, a 1st chorus, a verse, a 2nd chorus (longer), an outro (not always). It is also agremented with 1 or 2 drops and/or 1 or 2 bridges to glue the parts. The result was a bit repetitive but if the track had a real catchy riff, it was really enjoyed on any festivals or dancefloors.
In the modern approach, there are few more complex arrangements, with few more verses, chorus and drops. The result is much shorter and less repetitive parts than the oldschool way. You can also expect for much more complex bridges to glue each parts. The technics to create the best arrangements possible is a real challenge and will ask you years of work.
But you are here to learn, it doesn't matter if you aren't the next Astrix or Electric Universe yet. You will learn all the different ways to build your tracks in the best way possible. After this masterclass, you will improve your skills weeks after weeks until you become a real psy-trance artist. Being patient in music production is the key.
Listen to this oldschool psy-trance track: "LSD" (by Hallucinogen/Simon Posford)...
... and compare to this modern psy-trance track: "Deep Jungle Walk" by Astrix:
Oldschool music was made on the fly...
One other important thing to understand about the difference between oldschool vs modern type of psy-trance, is definatly the way the music was made in the early ages of electronic music. A world that most of the young generation will never know, a time where mistakes and errors were very oftenly responsible of a successful hit. No DAW, only multitracks recorder/sampler and some dynosaurus analog synth such as YAMAHA CS80, PROPHET 5, MOOG MODEL D, and of course the whole ROLAND synths such as JUNO-106, SH101, JUPITER, JP8000 and the legendary TB-303. In the 90's, making and recording from drums machine was a real challenge too... Using a TR-707, 808 or 909 was a real fun but not so easy to produce as today. Live recordings were the key... always improvising and feeling the beats to see if something nice could happen... And to finalize that recording, they were using some analog tape recorder for even more dirty sounds results. That was reality of electronic dance music productions in studio at this time. Perfection does not exists in this world, fortunately!
Watch Simon Posford in his studio in 2008, just when started transition between oldschool and modern world:
Nowadays, the FX plugins and VST instruments softwares are still trying to emulate all those dirty sounding treasures and it sounds really nice and warm, but keep in mind they are digital emulation only and the warm of the oldschool time has gone in software world. Of course, if you are enough rich, you can build an analog studio, with mastering hardwares, analog synths, tape recorders, etc... But I think this is not the way to make a career of Psy-Trance DJ/Producer nowadays.
Anyway, No matter how you will proceed to compose your psy-trance productions, the result must be always the best musical story possible, catching your audience and make them dancing on a dancefloor. We live in 2020, we must respect the past, but we must define the future of our music, with our new machines.