The skills you need depends upon the people you end up dueling. I can tell you to put all your points into reflex but if you are fighting a lot of melee players that won't do you any good. I can say put lots of points in tactics, but if you aren't being challenged that often then that is sort of a waste. I can say put them in appearance, but if you aren't challenging people often it is a waste. It depends on your play style, personal preference and the opponents around you. So read the guide, read the help file and learn from dueling experience.
I suggest putting 2/3 of your attributes to dexterity, and 1/3 to charisma. Its not good to put equal points on shooting, reflex, appearance, and tactics, you'll get bonuses from clothing anyway to supply those skills if you ever lack them.
Dodging benefits you from both melee and firearm attacks from the enemies but it does not lower the damage when you're hit, it only lowers the chances of you being hit at all. However this skill is not needed in any jobs.
Reflex protects you from all firearm attacks. Its not necessary to put around 25 points on this one without gear if your clothing can make your reflex up to 50 anyway. 50 reflex can lower the attack of a firearm wielding enemy with around 100-110 points shooting to only 75-90 if they are using a precise revolver no. 1 or about 35-90 using a precise pepperbox. Reflex is however needed in some jobs. Like what Denisero said, it won't do you any good against melee users.
Toughness makes you resist attacks from a melee user. The step is just like reflex is to shooting. It won't do you any good against firearms.
Aim increases your chances of hitting the enemy regardless if you are using a firearm or a melee. Its not needed for any jobs anyway.
Shooting increases your damage while using a
firearm. A high number of shooting, pushes the ability of your firearm weapon to its best. You should have at least 110-115 points on shooting once you reach around level 55. Its also cool to hang around with some good jobs.
Vigor increases your damage if you are using a
melee weapon. A high number of vigor makes you hit hard with a melee weapon.
Appearance is not a major skill needed for attack on dueling. Its very important if you are the
challenger to a duel and you should have high appearance if you are challenging someone with high tactics especially a
soldier with tactics advantage. I think it increases your chances of hitting your enemy as well once you are the
challenger to the duel. This is also good to focus on if you are looking for quite good jobs as well. Its good if you have around 50 points on appearance if you are around level 50.
Tactics saves you from taking too many hits once you are the defender in the duel. Its also needed in some jobs. If you do not want to waste skill points on this one, you better sleep once you are doing nothing or if you see someone camping in your town.
This is what happens on a duel.
Challenger's Appearance vs. Defender's Tactics
Shooting vs. Reflex
Vigor vs. Toughness
Aim vs.
Dodging
