It's a bit like going for your best time on old school mario kart, if you mess up at all, restart, concentrate on one level at a time.
You can only have 30 ghosts on the train at once, so once it's full don't waste time going round the long way to get more, just rush through clearing the screen.
The later into the level you get the more ghosts spawn in the trap - these ghosts can also join the train, when they do - more ghosts will spawn in the trap to replace them - so you can take shortcuts later in the course as some of the ghosts you miss will be replaced by ones from the trap. Try and track as extras have joined so you know what shortcuts you can take
Make sure you have a route that keeps both sides of the course at the same pace so when you get to the high scoring boards both sides match up to get the most points. Try and take routes that don't leave you waiting for your trail of ghosts to get out of the way.
Practice at hitting sparks of every wall you go along without accidentally turning when you don't want to - the time you gain from this is very small (i think only about 3-5 secs over 5 mins) and only worth it if you can do it without messing up at all.
Use a bomb rather than die - expecially if you are about to hit a power pill as it will replenish any game speed you lose almost straight away.
If you initiate the slow motion slowdown effect by getting too close to a ghost - ghosts that are on course to hit you will usually turn away at the next opportunity - sort of like a mini scatter effect (they won't turn back on themselves unless you hit a power pill though).
Don't try and prolong the power pill effect after you have eaten all of the train and any lined up ghosts on the course, let it run out so you can build up the train again as eating single ghosts costs a lot more time and means that other ghosts won't follow you and leave their posts while the power pill effect is still active.
Thats about all i can think of.