Good question. I'm curious about this as well as I'm only just experimenting with this.
Generally, I still leave it to the AssMan but make the occasional change prior to upcoming games. I do think the standard sessions are a little too generic and, whilst it stops overall stat drop, it doesn't target those important attributes at those low levels. not a dig; just room for marginal gains.
The other problem I have at that level is it takes an age to get team cohesion up to even a moderate level. Poor players playing poorly together: Nightmare fuel.
I've not planned this out extensively but overall it goes something like Pre-season (mostly leave to AssMan) > Match prep/squad cohesion work > Key attribute focus.
During early phase 2 I will have two match-prep style sessions (Tues = Overall + Match Practice) (Thursday = Outfield + Teamwork). Tuesday is a heavy day so that I gradually will start changing Match Practice to maybe the attack or defend match prep variants.
Once I'm happy the team is playing sufficiently as a unit or at least until its not a negative then its onto player key attribute focus. I break a month's 8 training days (counting 1 game/week) up to focus on Attack, Defend, Tactical and a Goalie/set-piece sessions. I try to make sure a training unit gets 1 session focus per day. I used to do these as 1 week all-attack etc. but found that the neglected units didn't train well that week and would flag up on training reports.
Not even looked at youth training but i'd probably leave out the match prep and crack on with attributes.
That's just my take on it. I hope it's at least logical. I'm looking forward to hear others take on it.