1. No two same-type damaging attacks on anything. It's pointless, redundant, and minimizes your options. Exceptions would be things like Endeavor, whose damage varies.
2. Recognize and appreciate the value of stat-raising and support moves such as Bulk Up, Calm Mind, Reflect, and so on. If you don't balance out your team with those types of moves, you'll probably get your butt kicked by a team that has them.
3. The typed held items, such as Mystic Water, suck. Don't waste your time with them. They only raise the power of attacks of their type by 10%, it's not worth it. Quick Claw also sucks, it only works 8% of the time. Again, not worth it.
4. For held items, you can't go wrong with Leftovers. I realize multiple Leftovers are hard to get without trading with other games and going through the battle tower lots, so Shell Bell is an acceptable alternative. Leftovers is always the best held item, unless your Poke has Rest, in which case the usual choice is Chesto Berry, or unless your Poke knows Thief or Covet, in which case don't have it hold anything.
5. Relying on legendaries on your team may be fun, and there's nothing really wrong with doing so, but don't claim to have any skill as a result of winning battles using them. Legendaries help you develop no skill whatsoever.
Feel free to ask questions, make suggestions, etc.
In-Game Hidden Powers by Toy
I am tired of people saying they dont want Hidden Powers ingame
Because it is to complicated or somthing here is and easy Hidden Power Guide
Fighting:Odd IV in HP or Atk
Flying:Odd IV in HP,Atk or Def
Ground:Odd IV in Def, Spd
Rock:Odd IV in SAtk
Bug:Odd IV in Hp, Def, SAtk
Ghost:Odd IV in Spd, SAtk
Fire:Odd IV in Atk, SDef
Water:Odd IV in Hp, Atk, Def, SDef
Grass:Odd IV in Def, Sdef, Spd or Atk, SDef, Spd
Electric:Odd IV in Atk, Def, SDef
Ice:Odd IV in Hp, Atk, Def, SDef, SAtk
Dark:Odd IV in Hp, Atk, Def, SAtk, SDef, Spd
those are the only useful hidden powers
there are differant variations and I will put them in eventually.
To make things easier teach one of the pokemon you are breeding Hidden Power so that each baby has it
http://www.serebii.net/games/hidden-power.shtml Main site's page on it.