I've been playing FM for years, but I have never really known how the simulations work. Is there a point to individually training attributes that aren't highlighted in the specific player's instructions role, or should I just train those?
For example, I always train my players individually to have high strength and acceleration(quickness) even if these attributes are outside of the highlighted player instructions. Is that a bad idea, or does it make sense to do?
Also, related to this : If a player has really low passing, should I train this attribute up individually even if it's not in his player instruction role?
What the game highlights for a position is just a recommendation. You should train players to be like you want them to be. The recommendations are a help, but don't let it be a hamstring.
If your player plays a lot of passes, he needs a good passing skill regardless of what his recommendations are. If you play a tough game, then stronger players will help your team in any position. Etc etc...
In the PL, if you want a skill (an attribute) to make a difference on the pitch, it will have to be in the "good" range for the most part. Since an attribute rarely improves much more than +1 per year for a very young player (21 or younger) and normally slower than that from 21 to 24, even if you select it as training focus, it is not very wise to allocate lots of time and resources to improve sub-10 attributes. Then it is better accepting that player's weakness and rather focus on making his strengths even stronger.
The exceptions are if A) that one poor attribute raised even to mediocre level will make the player well rounded, and B) It's Strength or Quickness
When a player is u23 I will tend to put a training focus on a physical attribute, be it strength, quickness or more rarely, something like balance. I have not ever bothered to teach players to jump, because I only really care about my CBs being fantastic leapers, and they should already be good at that by 21/22.
When they are 23-27 I will focus on technical or mental attributes, but when a player is starting to age around 31/32 and I want to see if I can slow down the decline of their physicals I will put their focus on quickness again.
I haven't had much luck training youngster's mental attributes, it needs to develop naturally, over time, and with game experience. I figure a player has a physical peak (around 24?), a mental peak (around 30-32), and a technical peak (27-28, but players don't decline technically as much as physically).