Help with training

What is the best way to improve the players in association?

A combination of setting practices to temporarily plus their ratings so you play better with them in games, development mode during the season for some small upgrade(s), and training camps during the off season.

Or you can cheat and edit the player.

i need to do only practice the shootaround and the all thing?

What is the red sign beside the player?
And If I dont choose specific player in the training so it does it for all the team?

development makes your players better. practice is only temporary.

What is the red sign beside the player?
And If I dont choose specific player in the training so it does it for all the team?

Don't know what red sign you are talking about.
Yes, the whole team.

Does training/practice affect the stamina of the players in-game? Making them more susceptible to be tired faster?

Yes, I believe so. When I practice too much, not only will their stamina decrease quicker in-game, but I have noticed that their performance will suffer. I usually notice it in the form of layups that miss short, and freethrows seem a bit harder.

What I usually do is practice on the normal setting. If I have a few games close together, I will use the light setting. When I have a stretch of a week or more without games I will do some intense practices. I am always monitoring their fatigue, though. I try to give them a day off every week, but if I have been doing intense practices, I give them atleast two days in a row before a practice or game.

What is the red sign beside the player?
And If I dont choose specific player in the training so it does it for all the team?

Don't know what red sign you are talking about.
Yes, the whole team.

This sign

I do allways practice and allways I have this sign

It means the players rating is lowered temporarily and the "-2" is by how much, so he's normally a 92. This can be due to a fatigued player, a player with low morale, or low team chemistry, an injury, and of course, a combination of all of them. I made somewhere around 20 trades in one day to free up cap space, and now all my players are like that because I have very low team chemistry. It's at 7% because I won 3 in a row somehow.

How many practices I need to do in week? I do every day and they very tired

Give them a few days off until they recover.