I just reached the E4 and I attempted to beat at least one member, I only knocked out one pokemon on his team. So here's my team right now.
TEAM:
Serperior Lv. 44
Grass Pledge
Slam
Giga Drain
Leaf Blade
Simipour Lv. 37
Surf
Bite
Scald
Acrobatics
Zebstrika Lv. 39
Discharge
Flame Charge
Pursuit
Spark
Gurdurr Lv. 41
Rock Slide
Wake-Up Slap
Strength
DynamicPunch
Victini Lv. 46
Confusion
Flame Burst
Quick Attack
Reversal
Any suggestions on anything would be greatly appreciated. Oh and where should I train my pokemon? On E4 members?
Wow, this team is seriously under leveled. By the time I got to the Elite Four, I was lvl 49+ for all my pokemon. I would suggest going back to battle any skipped trainers/ optional areas. From there, I trained to lvl 50 in the Elite 4 cave. Now about the team:
Serperior:
Scrap Grass Pledge. I cannot stress how useless this move is without the other starter pokemon on your team. Also trash Slam and teach him Return, much better accuracy and power. Since I picked Emboar, I don't know much about this grassy snake. But, I do know it has a poor movepool, so try to get it as diverse as you can, not with just 3 grass attacks and a bad normal one. I would suggest Leaf Blade, Return, Aerial Ace, Toxic.
Simipour:
Same problem as above pretty much, two many water type attacks this time. All I can say is to keep either Surf or Scald, not having both. Surf for power, Scald for high status inflicting chance. (I suggest Scald). Bite isn't a very good attack, but it's decent I suggest Shadow Claw, for the high Critical Hit change, but it's your team so good luck on that. For the last move, I suggest Rock Slide, but if you don't have that, then Brick Break.
Zebstrika
You made a common mistake. This guy is a PHYSICAL attacker, with medioce special stats. Keep Spark and Nitro Charge, those are keepers. BUT, you need to trash Discharge and possibly Pursuit. In place of Discharge, get Wild Bolt, and in place of Pursuit give him Stomp.
Gurdurr
First things first, trade this sucker over and get it traded back. Conkeldurr is MUCH better then his pre-evolution. Rock Slide is good, but Stone Edge is better. But the poor amount of PP it has isnt. Trash Strength for Brick Break or Hammer Arm, if you don't mind the speed drop. Poison Jab is on OK move, but really is only good for grass pokemon. For the last move, I would give him return, but after the Elites, give 'em Earthquake.
Victini
Hmmm. I'm not very familiar with this one. I know he has some powerful signature move, so get that, if possible. Psychic is a must, in place of confusion. Quick Attack and Reversal? Come on now, trash those for something else.
Sixth Pokemon?
What concerns me, is that the fewer pokemon you have, the higher your levels should be. When I had 6 pokemon, I was in the 49's before the Elites, You have 5, but barely average 40's! Train to at least 55 for all your Pokemon, since you only have 5, but also consider getting a sixth guy. If you're feeling lazy, just nab a pokemon in the Elite 4 cave. It comes coupled with a lvl 40+ lvl so thats fine too.
Overall, just keep on training! All the moves I mentioned should be available by level up or by move relearning. Don't go parading into the Elites just yet. Again, make those move changes, evolve your Gurdurr, and stock up on X items, revives, and Potions, because even I barely made it out the first time.
Just a heads up though, stock up on some ultra balls (unless your using your masterball) because after the elites, you face off against your Legendary Dragon! After that, you face off against the two most powerful trainers in the game thus far. (Not telling you for Spoiler purposes.) Be prepared for that!
Good Luck!