IncreaseScore(playerid, 1); //Increase player's score by 1
DecreaseScore(playerid, 1); //Decrease player's score by 1

instead of:

SetPlayerScore(playerid, GetPlayerScore(playerid)+1);
SetPlayerScore(playerid, GetPlayerScore(playerid)-1);

stock IncreaseScore(playerid)
{
        SetPlayerScore(playerid, +1);
}

stock DecreaseScore(playerid)
{
         SetPlayerScore(playerid, -1);
}

stock IncreaseScore(playerid, amount)
{
    SetPlayerScore(playerid, GetPlayerScore(playerid) + amount);
}

stock DecreaseScore(playerid, amount)
{
    SetPlayerScore(playerid, GetPlayerScore(playerid) - amount);
}