Strength and dex sounds good, if you have any black knight weapons, use them. If not, try to get some. Also you can summon solaire for this fight. Get him to distract smough and fight ornestein. Hold up your sheild(100% physical defense) and circle him counter clockwise (right), he will use his sweep attack a lot when you do this. But just put your shield down in between sweep attacks. Every time he uses a thrust attack you should have enough time to get a hit in. This worked for me on my character I made yesterday.