I also have been wondering this but I do not think there is a lot of advice out there for it yet. But here are a few things I have been doing. Take these with a grain of salt as I am only a season and a half in from a game I imported from FM23 on my Switch.
During preseason, if you put the training to be handled by your assistant, they are able to have preseason training while you are unable to select this option normally. I am unsure if this is better than selecting to train physical (Or even anything else entirely).
For big games, I usually try to have big matches trained the week before and the week during.
Change the intensity schedule and adjust it according to your schedule congestion. I usually have 2 games a week, so I have from condition very poor to condition excellent None/Half/Half/Normal/Double but I would probably have this be more intense if I only had one game a week. Using this, I no longer have to manually send my players on vacation for a day after every game.
If you decide to let your assistant control it, I would say to keep an eye on what they decide to do. Especially during big game weeks. I once had my assistant choose to do physical training when we had a champions league knockout game and a game against a rival during the same week. I had to do a full rotation for the second game as I noticed it too late.