Playing as Southampton using a 4-2-3-1 formation, I'm only in pre-season but I have found it best to give each of the three very different roles, so that they don't all try to fill the same space and do the same thing. I started off with a narrow three, but they kept running into each other and passes would bounce off the heels of a teammate facing the other way, so I spread the three across the width of the pitch. It has solved that problem, and it gives the two central midfielders more passing options, enabling them to offer themselves again to maintain possession when we need to be patient.
I have multiple players to fill the roles and I have been rotating, so here's how I have been using them so far, with some success (albeit only against average Italian and Swiss sides on my pre-season tour). I try to maintain a balance within the team while exploiting the individual skills of the relevant player:
Pablo Osvaldo - Wide Target Man; Left or Right; Support
Adam Lallana - Inside Forward; Left; Attack if opposite Osvaldo / Support if opposite Rodriguez or Isgrove
Gaston Ramirez - Attacking Midfielder (Support) or Advanced Playmaker (Attack); Centre
Jay Rodriguez - Inside Forward; Left or Right; Attack
Steven Davis - Attacking Midfielder; Centre; Support
Lloyd Isgrove - Winger; Right; Attack
Rickie Lambert - Attacking Midfielder; Support (encouraging long shots)
I have just signed Thomas Ince from Blackpool for ?3.2million-plus-Guly do Prado, and he seems best-suited to a byline hunting Left Winger role, or a right-sided Inside Forward, both with the Attack option.
My full-backs are playing with Support duty, but are encouraged to deliver crosses and I have the team detailed to float crosses, with Lambert, Osvaldo and Rodriguez all quite good in the air.
I played Schalke in one of my friendlies. They had Draxler on the left of their three. He ran at Nathaniel Clyne, cutting inside onto his right foot and smashed it into the top corner from outside the area - so you might encourage him to do more of that sort of thing in your game. Jefferson Farfan was on the right hand side and benefited from several early crosses from the left back putting him in one-on-one situations with Artur Boruc. Meyer was in the middle of the three. Klaas-Jan Huntelaar was operating as a Poacher or possibly an Advanced Forward and was very mobile. Final score was 4-4. I don't set opposition marking/tackling instructions for friendlies because the rate of substitutions make it impossible to keep up, but I would have done so for a competitive match.