I've always held my knife in my right hand because I'm right handed and have more control over getting the food to my mouth and not straight into my eyeball. The same rule applies to any type of cutlery if only one item is used. The fork if used on its own is used in the right hand. The rule becomes slightly harder for noodles though, I use a spoon and a fork, fork in right hand. Someone once insisted I used my knife and fork the other way around so out of politeness I did but after about 30 seconds I unconsciously switched them back and didn't realise :/