I know my first team, with the key positions having two first team players rotating. For example:
GK: Mandanda (Reina bench warmer)
RB: Rafinha (Opare as back-up, plays in high tempo games)
CB: Carragher (Agger as rotation)
CB: Zapata (Hobbs as back-up)
LB: Insua (Dossena as back-up)
RM: A.Young (McBride as rotation, as well as Elano)
CM: Mascherano (Zobel and Lenny as back-up)
CM: Gerrard (Mascio as rotation)
LM: Mata (Robinho as rotation, Babel too)
ST: Davies (Babel, Kuyt are rotations)
ST: Torres (Babel and Kuyt are rotations)
I have a few versetile players. Babel is happy, as he plays on right, left, up front he gets a good amount time on the pitch as well as Kuyt. My wingers are the key to my tactics, with a good work load. So a rotation is neccesary. Elano, Kuyt, Babel, Mcbridge, Robinho, Mata, they are all there if needs be. Elano is leaving at end of season anyway, he's about 32.
The central midfielders, the main two is Gerrard and Mascherano. Mascherano plays near enough every game, but Gerrard is getting on in years now and tires quicker. So I have cover for him, these are young players who will be first teamers in a couple of years.
Opare is young and likes the amount of games he gets, which is about 1 in 4. Dossena is leaving at the end of the season, he gets about the same. Carragher like Gerrard gets tired easier, so I rotate him with Agger and Hobbs. They're happy.
What I have done in my years, is let those in their prime age be the first teamers (As they are best) where as the older players who will be leaving have a shared amount of game time as the young players breaking through. Players like McBride, he gets a bit more time than Elano as he's (One better) but Elano is leaving.
I may sound like a un-friendly manager. But unless the older players hitting their 30's have great stats, I give them less time on the pitch. But use them as impact subs. So the young players who have a future come through, get some game time and if there is any injuries, well they're there to play.
It's good to have versetile players in key positions. Babel and Kuyt are brilliant for this. Babel can hold up the ball, run down the wings, run through the middle, get onto through balls. He's surprisingly brilliant in the game. Kuyt is getting on now, but he can play in key positions. So he gets good amount of game time.
Gerrard is out for rest of season now, 2 months to go. So Lenny (Great regen, amazing free kicks, scores 1 in 3 from any distance) has come in and rotated with Mascio. So I have two great young players happy.
At times I don't know how I do it myself. I have a great squad harmony, and even Reina is happy despite playing only 14 games this season.
Also, for the players leaving. Elano, and Dossena. I can give McBride more game time with Kuyt as his cover if needs be. While I have two good young left backs coming through the youth academy to replace Dossena. Both predicted to be leading stars. I can see Insua leaving in four years with them two young left backs fighting for their place in the team.