to beat the elite 4 you should have all Pokemon above lv 50. you should also carry a lot of revives
Anywhere
defeat the elite four
Nope, sorry. You have to get the national dex and you can only get it if you defeat the elite 4. (and Cynthia)
You have to get all 7 Gym Badges, beat the Elite 4, and defeat the Champion, Cynthia.
after you defeat Cyrus you can battle dialga then you battle the three lake Pokemon and move on to sunnyshore city. then you go on to defeat the elite 4.
After the elite 4 (in Pearl Diamond or Platinum) you need to go into the big room and find Cynthia and defeat her and go to professeur and get the national if you have seen all the Pokemon in the sinnoh dex
To defeat Team Galactic, complete your pokedex, and defeat the Elite Four and Champion.
train
You don't need to defeat the Elite 4 20 times, your rival is at the Fight Area every Saturday.
You need to defeat the elite 4 and Cythia and then go to snowpoint city and you can go on the boat just down from there
victory road
FireGrassWaterGhost or DarkElectricRock or Grond