Good Training Methods Pre-E4?

Venusaur
Frenzy Plant
Razor Leaf / Giga Drain
Sleep Powder
Sludge Bomb / Leech Seed / Toxic

Sleep Powder can be obtained via move re-learner, really useful to shut down enemies as Venusaur's nearly always going to be hit first. But once they're asleep you can take care of pokémon with Razor Leaf or Giga Drain. Save Frenzy Plant for when you're either against their last pokémon or think you're screwed anyway.
I personally go for Giga Drain and Leech Seed to keep replenishing Hp. But it looks like you taught Golbat Giga Drain, so stick with RL. Toxic is good in that even if they switch they're still affected. Whereas Leech Seed means that if you switch / get KO'd your next pokémon can be healed every turn.

Nidoking
Ice Beam
Megahorn
Earthquake
Thunderbolt

Nidoking's so versatile, but at least give it Earthquake instead of Dig to hit harder. Thunderbolt / Ice Beam between them hit every single pokémon in the game neutrally, and can get you super-effective hits against most of Lorelei's team and all of Lance's, as well as Gary's Charizard.

Golbat
Toxic (if not on Venusaur) / Facade / Secret Power
Aerial Ace
Steel Wing
Giga Drain

Facade / Secret Power makes use of Golbat's higher attack stat compared to Bit (special). The others look allright for in-game tbh.

Swalot
Toxic
Body Slam
Sludge Bomb
Stockpile

Swalot's basically a tank, so use it that way. Toxic to deplete their health, Stockpile to help maintain yours. Sludge Bomb is STAB, Body Slam can paralyse and also hits harder than Strength. And these are all level-up moves, so you don't need to use up tms (provided you have mushrooms)
From tutors you can also get Double-Edge, Explosion or Substitute. If you wanted to go real stallly (which I wouldn't personally due to impatience, but you maybe could) then try Substitute / Toxic / Sludge Bomb / Stockpile.

Haunter
Hypnosis
Shadow Ball / Thunderbolt / Giga Drain
Dream Eater
Psychic

You'll definitely have enough Sludge Bomb in this team, go Shadow Ball. It can lower special defence, giving Psychic more power. If you don't put Thunderbolt on Nidoking, give it Thunderbolt instead, much better to use your special attack stat. Or if you somehow have Giga Drain available, that's still better than Shadow Ball or Sludge Bomb off that 50 base attack.

Tentacruel
Surf
Barrier
Blizzard / Ice Beam
Rest

If you've used Ice Beam on Nidoking (you should), get Blizzard. If you've got a Chesto Berry, use it in case you need to Rest against the Champion. Barrier gives you durability anyway.