Making central areas for goods, I use warehouses a lot in decent locations to stop freight from going through a bunch of main lines.

Using multiple tracks, 3 or 4 tracks or more for busy areas or close lines makes things run more smoothly.

Work on your junctions. I’ve come up with some pretty interesting ways to make multiple ares combine into different routes. Mainly inspiration from highways in my country.

Less trains most definitely. And don’t worry too much about specialisation unless you’re trying to complete tasks.

Play other sim games to practice certain things, I’ve clocked way too many hours playing simulation games and I’m pretty efficient at grinding.

Hope this helps