1.How do you select your starters, Skill or Form or Fitness?
2.Would you play your star player even if he has been performing poorly for the past few games?
3.When do you substitute a player, when he is tired or when he has been performing poorly?
I have something like a base lineup based on skill, value, and how I like the players. This is the default lineup which I think is the best I can come up with, if everyone's healthy and in form, and match fit.
Example from Real Madrid: Benzema (ST), Kaka (AMC), C. Ronaldo (AMR), Di Maria (ML), Xabi (MC), L. Diarra (DMC), Lahm (DL), Sakho (DC), Pepe (DC), Ramos (DR), Casillas (GK).
Then I have the default 7 guys on the bench, to cover all the spots, if someone gets injured or is exhausted during the match.
Example from Real (I included the guys they can cover for in the brackets): Adler (Casillas), Arbeola (Lahm, Ramos), Albiol (Sakho, Pepe), Moussa Sissoko (L. Diarra, Xabi), Marcelo (Di Maria, Lahm), Granero (Kaka, C. Ronaldo, Di Maria), Higuain (Benzema, C. Ronaldo, Kaka).
So this way I can replace every spot in my lineup easily. This is the selection I start with, and I change it like this:
1. If someone's injured, I will of course replace him. If someone from starting lineup is injured, I will put someone from the bench to the starting lineup, and move someone who was not in the selection before to the place on the bench (these are the backups I don't use regularly, for example M. Diarra, Raul, S. Canales, Chema Anton etc).
2. The starters which are level above their replacements play almost every game. These are C. Ronaldo, Kaka, Lahm, Ramos, Sakho, Casillas. I only put them down if they are injured, or if I play more matches in less days, and they have fitness below 90%, and/or it's an easy opponent, and I want to rest them for more important match. I play them even if they don't play very well, because that usually lasts only one game, and they play well the next game.
3. Players for which I have very good replacements, almost with the same abilities, I rotate. These are Benzema -> Higuain, Di Maria -> Marcelo, Xabi -> Sissoko, L. Diarra -> M. Diarra, Pepe -> Albiol. The way I do the squad rotation is that I replace only one of these players every match, and keep the rest of the squad as was the match before. So usually everyone will play like 5 matches before their turn to sit down comes again.
4. All that was said before is the "perfect" example when everything is going alright.
But they are slight changes if someone performs very poor for 2-3 matches, I replace them immediately. In the other hand, If someone is performing very well, like scoring hattricks, I keep them in the lineup even if it's their turn to sit down.
4.What level would you define a player tired (level in % of match fitness 1-100%)?
I rarely use players that have fitness level below 90% before the match. Only if I play a strong opponent, and it's someone like Kaka, or C. Ronaldo. During the match, I usually try substituting players which have less than 70% 60-70 minutes in the match.
5.When would you play your reserve squad players/back up players/youngsters?
Very rarely, only if I have a lot of injuries, or someone from them I don't want to upset (hot prospects) keeps ******** he wants to play. Otherwise I don't care about them much.
6.How many games will keep a player happy per seasons( the minimum number of games to keep a player happy) ?
I don't know the exact number for this. Depends on the player. Someone is happy to play one match in a month, or just if you play him in the cup. But I'd guess someone like C. Ronaldo would not be satisfied with that.
Thats about all i want to know, thanks for the help
Hope it helps.