[Avi Raj]

Code:

public OnPlayerDeath(playerid, killerid, reason)
{
    SendDeathMessage(killerid, playerid, GetPlayerWeapon(killerid));
    SetPlayerScore(killerid, GetPlayerScore(killerid)+1);
    SendClientMessage(killerid,0x00FFFFFF,"Good Job, You Got 1 Score For Killing a Player");
    SetPlayerScore(playerid, GetPlayerScore(playerid)-1);
    SendClientMessage(killerid,0xAA3333AA,"You have Got -1 Score for getting killed By a Player");
    return 1;
}

It have client message too which will be sent to both Killer and Player.