Bulbasaur can be found at Cerulean City, near the Pokecenter.

Charmander can be found at Route 24 N.W.

Farfetch'd can be found on Routes 12 and 13.

Magnemite can be found in grass before the rock tunnel entrance.

Get the Thunder Badge on the S.S. St. Anne, then go to Vermilion City to find Squirtle.

When you have reached the mystical bird (Arcticuno, Zapdos, and Moltres), save the game before going into battle. This will allow you to restart if you knock them out or run away.

Note: The Pokémon Stadium game on the Nintendo 64 is required for this trick. Successfully complete the tournament mode on Pokémon Stadium without using any rented Pokémon. Then, transfer Pikachu to the Pokemon: Yellow Edition cartridge to play the Pikachu surfing mini-game.

Note: This trick requires a Game Shark cartridge. Use the following code to unlock Surfing Pikachu without using Pokémon Stadium. Note: Pikachu must in the first position, then use one of the following codes:

013972D1 (To overwrite the first attack with Surf)
013973D1 (To overwrite the second attack with Surf)
013974D1 (To overwrite the third attack with Surf)
013975D1 (To overwrite the fourth attack with Surf)

This will not glitch the game if you set the switch to normal and turn it to on after the game starts. To play the mini-game, simply travel to the Surfing Guru south of Fuchia City and talk to him.

Another method is to trade Pikachu to a Red version of the game. Use the GameShark code on that version of the game to teach Pikachu Surf. Then, trade Pikachu back to the Yellow version. Travel to the Surfing Guru south of Fuchia City and talk to him.

Your Pokemon can be printed at the Pokemon Club in Vermilion City.

Catch a Caterpie in Viridian Forest. Advance it to level 7 and he will evolve into a Metapod. Advance it to level 11 and it will evolve into a Butterfree. Butterfree can beat JR. Trainer and Geodude. Butterfree will have to be at least level 13 before it can beat Brock. Note: Use your Pikachu's tail whip to lower their defense.

To find these team rocket members, go to these locations:

Mt. Moon (before you exit)
Celadon game corner (before you face Giovanni)
Pokemon tower, Lavender Town (before you rescue Mr. Fuji)
Sliph Co. (before facing Giovanni again, and before you get a Master Ball)

 
Since i could not find that many cheats and hints for yellow i added this part it is a glitch no a cheat or hint
 
There are trainers in the game with a maximum visual range of 1/2 the
screen's length. The moment they pop up from a side of the screen,
they challenge you. These trainers have a very slow response speed.
This means that, when you find such a trainer and it comes within your
screen area, if you move fast enough, you can do an extra action before it
challenges you(i.e. move out of the way or activate the START MENU).

STEP 1:

Stand close enough to one of these trainers so that if you take one step
towards them they will pop up from a side of the screen and challenge you.
Take one step in their direction AND WHILE YOUR CHARACTER IS TAKING THAT STEP
PRESS AND HOLD START. The MENU should pop up at the very moment when the
trainer appears. He will not have enough time to challenge you and will
wait until you close the START MENU.

STEP 2:

Using the START MENU, exit the area(route etc.) in which he's in via any means
necessary(i.e. TELEPORT, FLY, ESCAPE ROPE, DIG etc.).
Notice how the trainer gets the "!" mark over his head and how the music
changes while you are disappearing. However, he won't have enough time to
challenge you because you will be transported to a POKEMON CENTER before he
has time to walk up to you.
NOTE: Later on these 2 steps will be referred to as the "LONG-RANGED TRAINER
      EVENT".

STEP 3:

Now, after you've gotten away, beat another trainer.(if you want mew then here use the trainer that i mention after these steps)
Notice how you are unable to use the START MENU or interact with people,
but you can still interact with hidden items and the PC.
The trainer you choose to battle with must have a visual
range of at least 2 map tiles(so it can walk up to you when it
sees you). Each trainer will generate a different POKEMON at STEP 5.
DON'T TALK TO THE TRAINER AND DON'T STAND DIRECTLY IN FRONT OF IT, OR THE GAME
WILL FREEZE! Instead, place yourself at least 1 step away from it.
After beating it, the START MENU will work again.
TIP: You can use the PC to save the game by changing the POKEMON BOX.
     By resetting and loading after that, the START MENU will work again.
     Use this little trick to fight trainers in areas you normally couldn't
     access without using the START MENU. But even after you enable it, you'll
     still need to beat 1 more trainer to get to the next step. However, now
     you can use any trainer, including special trainers like GYM LEADERS or
     your rival. But you still need to stand 1 step away from trainers that
     have a visual range.
If you want the POKEMON generated at STEP 5 by a trainer you can't reach
(i.e. a girl in ERIKA's GYM, and you need CUT to get in, but you can't access
the MENU to use it), beat another trainer you can easily get to(or use the PC
saving trick), then go to the other trainer that you couldn't
reach, because the START MENU will now work again.
Saving at this point, resetting and loading will NOT corrupt the savegame.
However, the events at STEP 5 will no longer occur.
NOTE: Using the PC to re-enable the START MENU will also allow you to battle
      trainers on the route with the long-ranged trainer. They will lose
      their visual range, so they have to be challenged by talking to
      them. If any trainer on that route says or would have said anything
      after losing(like the ROCKET on NUGGET BRIDGE on ROUTE 24), that
      message will appear on screen, regardless of what trainer you've beaten,
      the "!" mark will appear again over the trainer's head and the game will
      freeze, so don't do this on routes which contain such trainers.
WARNING: Battling a trainer on the same route with the long-ranged trainer
         will cause strange sounds on the background and a lot of pausing,
         making it very difficult to move around. Try pressing "A" or "B" at
         times if the game seems to be frozen. The MENU can still be
         used...after pressing "START" a few(?) times, and sometimes messages
         like "1 ERROR" appear. Sometimes, the MENU doesn't want to activate
         at all, and you'll have to battle a POKEMON to(maybe) re-enable it.
         There are also times when the game will simply freeze.
         The effect is permanent, so don't save if you ever want to use that
         route again! Also, the game will halt if you beat yet another trainer
         on that route after enabling this effect!

STEP 4:

Return to the long-ranged trainer you triggered at step 1.
NOTE: Do not go to the VIRIDIAN GYM during this time, unless it's open, as
      the game will freeze at STEP 5. Even as much as looking at the locked
      door is enough to trigger this unwanted effect.
The moment you enter the area in which he's in, the START MENU will pop up all
by itself. Do something to close it(FLY, TELEPORT, ESCAPE ROPE, DIG etc.,
or simply press "B"). It doesn't matter what you do, your
actions from here on will not change what will happen in the next step.

STEP 5:

A POKEMON battle will start. Run, catch it, or make it faint.
This "surprise-POKEMON" that appears depends on the SPECIAL of the last
POKEMON the opponent used before getting beaten.
The surprise-POKEMON will always be at level 7.
NOTE: The long-ranged trainer you triggered can still be fought, so you can do
      this trick many times over with different trainers.
      Some of these surprise-POKEMON may be very rare, unique, and some may
      not even be in the version of the game. For example, GROWLITHE is not
      in the BLUE version, but can be obtained in it using this trick.
      The only downside of this procedure is that it can be done a limited
      number of times(until you run out of trainers). However, you will
      find different tricks below that are based on this procedure, but can
      be done without the use of additional trainers. These tricks will
      further narrow the requirements and enlarge the number of POKEMON that
      can be obtained.

!!IMPORTANT!!

It doesn't matter which trainer you've beaten first. The
surprise-POKEMON will always depend on the trainer you beat last.
if you want mew you have to use the youngester on route 25 the one with the level 17 slopoke this is the trainer i mentioned on step 3