[DaRk_RaiN]

Well there are a lot of ways, here are the easiest
In case you didn't use the fonctions SetPlayerTeam and GetPlayerTeam,and used gTeam instead use them, its the best way to prevent Team Kill
Example:

pawn Код:

OnPlayerSpawn(playerid)
{
  if(gTeam[playerid] == TEAM_ONE) 
  {
   SetPlayerTeam(playerid, 1);
  }
  else if (gTeam[playerid] == TEAM_TWO)
  {
   SetPlayerTeam(playerid, 2);
  }
//ect..................
  return 1;
}

And there is an other simple way to do it using OnPlayerTakeDamage CallBack

pawn Код:

public OnPlayerTakeDamage(playerid, issuerid, Float: amount, weaponid)
{
    if(issuerid != INVALID_PLAYER_ID && GetPlayerTeam(playerid) == GetPlayerTeam(issuerid))return 1;
    return 1;
}

And in case you use gTeam

pawn Код:

public OnPlayerTakeDamage(playerid, issuerid, Float: amount, weaponid)
{
    if(issuerid != INVALID_PLAYER_ID && gTeam[playerid] == gTeam[issuerid])return 1;
    return 1;
}