Tips/Advice for a Playthrough of Pokemon FireRed/LeafGreen?

Question

A thread for posting (spoiler-free) advice for a playthrough of the given game which will help anyone playing it. The aim of this thread is to make playthroughs easier for someone who is playing it for the first time.

A couple of rules:

1. Don't give advice for Pokemon as a whole. Seperate thread for that can be found here.
2. Try to keep advice beginner friendly. Do not go into the more complex mechanics.
3. Don't post multiple answers. Edit your existing answers to add more.
4. No repetition

Answer 1

In FireRed/LeafGreen, there's a lot of competition on who gets what TM on a playthrough team. Not only are there Pokémon who rely entirely on them for their movesets (Clefable and Starmie), but also ones who need them to work off their higher attack stat (Gyarados and Haunter/Gengar), along with those who don't receive all their STAB moves through level-up (Jynx). This is especially important for these games, as there'll be a lot of overlap over who gets what. Whether or not a Pokémon can access specific, non-reusable TMs can make or break them.

This might be hard to take in thanks to favoritism, but all the starters in FireRed/LeafGreen come with their own ups and downs. For Bulbasaur, though it has a good early-game, it relies entirely on good matchups to prove useful, which is worsened by Grass typically being resisted in Kanto. Charmander similarly has an excellent mid-game, but that's traded for a rough early-game and a passable late-game. Squirtle performs the most consistently, though there are a plethora of Water-types that also serve this role, as opposed to the latter two starters. Take note of this when teambuilding.

Pickup Meowth can be caught before Misty with a 5% chance of its Pickup item being Rare Candy, PP Up, or a Nugget. You may also get Berries or the Hidden Power TM, but these aren't as useful.

Comments

It's probably worth mentioning that if you use certain Pokemon like Charizard, Clefable, Gyarados, or Arcanine, you'll want both STAB moves and moves for their higher attack stat, because either of them can do more damage depending on the opponent's types and defense stats. If you use Haunter, don't use any STAB moves

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Yup, that should no doubt not go unmentioned. In fact, I sort of alluded to that when discussing TMs.
I think Haunter can still make good use of Shadow Punch/Shadow Ball against Psychic-types with low Defense, though it no doubt makes better use of moves like Psychic, Thunderbolt, Hidden Power, Giga Drain, Hypnosis, etc.

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Don't use hidden power in gen 3. Its base power can be anywhere between 30 and 70.

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I genuinely did not know that.

Answer 2

• On Route 25, there's a Secret Power TM normally locked behind a cut tree and a camper boy. This TM can be quite useful earlier in the game, especially if you're using mons like Fearow or Pidgeot that can't get better Normal moves this early otherwise. You can actually get said TM before getting Cut by getting the camper to move out of the way. To do that, all you need to do is to enter the Camper's line of sight, while being at least 2 tiles away from him. This shouldn't be too difficult to pull off, but you can always just save beforehand and reset in case you mess up. (Note: This trick also works in RBY and LGPE to get the Seismic Toss and Thunder Wave TMs, respectively)