Go to Routes 24 and 25 north of Cerulean City
Use a Pokémon with a move that can inflict sleep or paralysis
Save before encountering Abra if you want to retry
Find Abra in tall grass on those routes
Use a Quick Ball on the first turn if available
If Abra uses Teleport, catch it before it escapes by using a faster Pokémon or a Quick Ball immediately
Use status moves like Sleep Powder, Hypnosis, Thunder Wave, or Spore
Lower Abra’s HP carefully if you can act before it Teleports
Use Ultra Balls or Great Balls after applying status
Repeat encounters until you catch one