Should have more advice in the instructions, or even in the help section of the game. Very quickly, though:
Pick the training category where you're the weakest and select that one (I usually go for tactics). Then:
Motivating and man management should be 18+ if you're a top team.
Prob best to have them high on working with youngsters if they're managing your U18s.
Additionally, my desire is for them to have at least 15 on judging players, judging potential, level of discipline and adaptability.
Scala, Pincolli, both good and likely to move if you have the wages. I think there's a physio called Paixo or something who has the right attributes.
My own assistant is retiring at the end of the season so I've pinched Joe Jordan from Portsmouth as a 1st team coach - he will be assistant for my 2011/12 season.