Smeargle is good if you have a large collection of different Pokemon to Sketch from, as you can get ANY moveset you want. Here's my strategy (it works for any category):
Slot 1: Move that doubles your score next turn. (Ex: Cool--Acupressure, Tough--Acid Armor, Cute--Amnesia, Smart--Defend Order, Beauty--Meditate)
Slot 2: Move that gets +2 Appeal if you move first (Ex: Cool--Dragon Claw, Tough--Lava Plume, Cute--Mirror Shot, Smart--Future Sight, Beauty--Aura Sphere)
Slot 3: Move that gets high Appeal for low Voltage: (Ex: Cool--Dizzy Punch, Tough--Lick, Cute--Guard Swap, Smart--Smellingsalt, Beauty--Feint)
Slot 4: Filler.
Disclaimer: I got the above information from my Prima Diamond/Pearl guide, which has a sickening amount of typos. So, some of it may be wrong. Check the move information in-game before you Sketch it onto your Smeargle.
First Round: Slot 1.
Second Round: If there is a judge with no Voltage, use Slot 3. Otherwise, use Slot 2.
Third Round: Slot 1.
Fourth Round: Repeat Second Round.
If your Pokemon has high condition in the category, is equipped with a contest scarf (I recommend sending your scarves from RSE via Pal Park, as getting them all over again on D/P can be difficult), and got good scores in Appearance and Dance, you're pretty much guaranteed a win.
I apologize to Moltres and all Divine Dragons members. You'll find my explanation on the first page of the clan thread.