Route 4 is a short path in north Kanto that expands from the Poke Center at the eastern exit of Mt. Moon in the west to Cerulean City in the east. Though the official western terminus of Route 4 is at Route 3 south of Mt. Moon's western entrance, the western terminus is regarded by most to be Mt. Moon's eastern entrance.
From Mt.Moon, Route 4 travels to the east, swerving to the north and the south to avoid ledges along the route. The path turns north, then east near a large clump of trees surrounding a grassy area. To the east of this area is a ledge that separates Mt. Moon from Cerulean. By hopping down this ledge, you won't be able to return to the previous towns until obtaining HM01Cut, coming back through Diglett's Cave and returning to Route 2.
The majority of the route is fairly straightforward as there is only one true way to proceed on the path and there are no trainers to battle (with the exception of a Lass on the highest hill on the route; however, she is reached only by way of the waterway that begins on Route 24).
Move Tutors
Name
Attack
Accuracy
PP
Type
Effect
Tutor
Mega Punch
80
85
20
Normal
No Effect
Left
Mega Kick
120
75
5
Normal
No Effect
Right
You may choose to use these Move Tutors to teach their moves and add some power to your team, but it is not recommended. You'll make changes to your team pretty soon, and as Move Tutors will teach their moves only once, using them now may be considered a waste.
In the Pokémon Center in the beginning of this route there is a fisherman that will sell you a very special Pokémon for 500. At first, Magikarp is the weakest creature in the entire game, with pitiful stats and only two possible moves (one of which is useless). When it evolves, however, it becomes one of the most invaluable and fearsome colossi of all the Water-types: Gyarados. Seeing as you can fish for Magikarp when you get the Old Rod a little later, getting Magikarp right now is quite a rip-off.
#23 Ekans
#27 Sandshrew
A Poison-type Pokémon that is exclusive to Pokémon FireRed. Its Intimidate ability is quite useful: it decreases opponents Attack. It evolves into Arbok. It is rather mediocre Pokémon since its base stats aren't that good and it doesn't learn many powerful attacks by itself.
A Ground-type Pokémon that is exclusive to Pokémon LeafGreen. It evolves into Sandslash, which packs a punch. It has nice Attack and Defense stats, but its Special Defense and Speed are quite low. It learns some useful attacks by TMs.
Items
Persim Berry (hidden in between the three rocks at the left of the PokeCenter)
Razz Berry (hidden in the grass southeast of the tutors, but before the jump off, near the trees west of tall grass. Look for a small, short dark line.)