there is no best way there is only your way.
The best way is challenge the elite four with your Pokemon or a Pokemon holding exp. share. The better is to use gameshark codes for rare candies.
The best psychic Pokemon on Pokemon diamond is alakazam. It can beat an infernape level 100. who carez about a dull looking Pokemon with two unusually big mustaches... ew... but I like Lugia and Espeon... and Gallade... and Gardevoir... bronzong all the way haha
you use diffrent types of Pokemon to get a advantge
It depends if you have a way you can cheat or not
there is no best way there is only your way.
the best would be to be with it always, and not let it die.If it loses some HP to care for it quickly. Also the Resort Area Club, 2nd floor massage which you can take once a day, will also help make them like you.Some items will also speed up the Pokemon liking you.
The best way to defeat them is to train your Pokemon. No Pokemon will be above level 50 or something like that. The 4 main elite four, their Pokemon are only in their forties.
You can not make a team. I have it and i played it like 5 times already and I can not make a team. The only way is to forget about it and buy another pokemon game. This one is bad.
The best way to hatch a shiny pokemon as of gen 5 is to breed 2 pokemon from two different countries.
Just put them in your party like other Pokemon. There is no specific way to use them. You just make them battle like your other Pokemon.
use your best pokemon and pokeballs
wifi is the best way.
the best way is to make something you would know but do it like this ex @d!3N
take your low level Pokemon to the Pokemon league and make shure they are first in your party then as soon as the get sent in you switch out to your level 100 giratina or something
Many way's like having it with you while walking and some kind of berries.
The best team is the Pokemon that you like the best! Another way is to pick a partner that has attacks that can protect you from your weaknesses. For example turtwig and piplup make a good combination because piplup's water type moves are good against the fire types that are good against turtwig.