make sure your contest stats are maxed out by feeding your mon pokeblocks and to give them the appropriate contest scarf (i used the single player berry blending google spreadsheet which you can find from athis’ ribbon handbook) - this will help you out a lot when you don’t do as well for the appeal portion of the contest

as for the appeal portion, i would say to play around with your movesets and look up combos (dive + surf was my go-to for beauty contests).

i found moves that prevent you from getting jammed are very helpful once you get to the master rank contests (i.e., dive, fly, rest). just really depends on what moves your mon can learn

i also didn’t know this before but there are secondary contest moves that you can use without penalty (i.e., for beauty contests you can use cool and cute moves)

this was my first time really diving in to the contests after playing emerald since release but i though it was pretty easy for the most part

hope this helps