if the favourite has been gradually drifting all morning, does this mean it is because traders are laying it or
because people are backing one of the other favourites? How would I be able to tell?
Trading
Hi Court, welcome to the forum. There's a multitude of reasons why the favourite or any horse might drift. Ultimately few people are backing it or there's money for the others. Possible reasons are that it's underpriced, a change in the going, tips released for another runner in the field, a negative report from the trainer, the failure of a short-priced stablemate in the previous race, etc. There is no easy way to tell unless you've heard something in the news.
The conditions a horse prefers are sometimes obvious and sometimes a matter of opinion (if a horse has never encountered the ground or has marginal preferences) and can be derived at by looking at a horses form or summary. It's been a long time since I was studying horse racing so I'm not sure what free services summarily state what going a horse prefers. The going at a track is listed in racecards like Sporting Life or Racing Post and you can check the weather forecast to keep up-to-date.
If you're a cold trader it's not absolutely crucial to follow form, and personally, as a former bettor, I think anyone who's new to horse racing and trading would simply be overloading themselves with more information than can be processed by trying to understand form. It really takes years of experience to have a good understanding of form and how to interpret it.