Just remember you guys some teams are exceptionally great i've came up with some examples
(Also if u didnt pick totodile for your starter, try the Gyarados from the lake because it have an AMAZING attack stat even without EV training)
It depends on the starter you picked I'll start with my personal favorite
If you picked Cyndaquil, your team, before the Elite four,would look like this
Typhlosion
Gyarados (i perfer this 90%, you cant find a good water type in this game. OR you can try the Lapras you can obtain every Friday in B2 Floor in Union Cave)
Any Flying type Pokemon (Pigeot or Fearow are good choices)
Any Electric Pokemon (Magneton, Jolteon(The Eevee Bill gives you into from a Thunder Stone) and my favorite, Ampharaos)
A Dragon Type pokemon (Who else but Dragonite)
ANYONE OF YOUR CHOISE (Rock, Psychic, Grass, or even an Ice type the pick is yours)
If you Picked Totodile:
Feraligatr
A Fire Type (Growlithe, woops, hes exclusive in HG, well you can evolve the Eevee into Flareon from a Fire Stone or a great one, Houndoom)
Grass Type ( Oddish>> Vileplume or Roselia, Cmon men you can deal with a girly Pkmn)
Flying Type (Mentioned above, Flying is important)
Fighting Type (Machamp, Hitmonchan/lee/top, pretty decent type)
ANYONE (I'm Always giving you a choice of your own)
If You chose Chickorita, which is rare b/c the first two are very loveable
Meganium
Gyarados/Lapras
Steel Type (Great type, love it. Steelix is probably the only one you can obtain so far)
Fire Type (This is a great type, again Houndoom, Growlithe or Flareon, oops i forgot, Magmar is great too.)
Rock Type (Has a pretty well type Pros and cons. Try Donphan, Rhyhorn, Golem, Onyx, etc
ANYONE ( a third time, your pick)
If this doesnt help, please comment below, and im sorry if i make a mistake.