AS a proud owner of a title "Trainer" i ll try give you some advices here
Basically is u have 250 pvp wins direhorn and you pair it with the right pets u ll have 70%+ win ratio.
Using 1 direhorn all the time is ok but in 5.4 u ll feel very stupid cuz your whole strategy will die :_)
So about advices part .....you want pets that can stand there ground no matter what enemy has.You want to use a combo of 3 pets where for example if you use a direhorn then you need a very hard counter to mechanical pets or if u use a weak humanoid like S/S Imp from kara(not Idol ...idol is not weak he can beat many undead pets 1v1 lol) then you need a strong undead to cover it.
You must have some kind of dot protection in your team (sandstrom,shell shiell etc),one or even 2 dodge skills are more then welcome especially if they are fast breed,even a single swap kills can change the outcome of the battle!When you see enemy team that has 2 or even 3 swap skills you need to time your moves so he swaps the right pets you want.Also vs team with a faster then swapper pets then your direhorn ...just spam that charge so enemy doesnt get a free turn.
Most of the combos i play are so predictable that sometimes even with strong attack vs me or me doing weak attack i can beat them .You can also play a team that is nothing special on a 1st look but its full of pets that counter the most popular pets.
Another great way to go is for pets that has strong attack vs what can counter you (undead pet spirit crab with critter attack ..u can play it safely vs critter....he will kill you fast but also you will do same
In your team you want at least 1 hard hitter 1 fast pet and 1 tanking/avoidance pet and if u can mix more then one of these in 1 pet while your other 2 pets....at least 1 of them cover your counters then you are good to win vs anything!
Another advice i can give you is to play with pets that have more then one valuable skill set combo so enemy are not quite sure what move you have before you use it(for example Idol is crush is a joke vs direhorns ....but with demolish is another story)
My last advice is dont be afraid to switch your pets a lot and dont let enemy trick you by beating him at start but then u left a very weak pet vs his last pet
p.s. no matter how good you bad you are ...when you miss 2 times a 95% move and enemy hits you 2 times in a row with 40% skills its GG ! ;xD