Now that you've obtained HM01 Cut (and possibly the Thunder Badge, although that's technically optional for most of the game), you can cut down the bush to the east of Cerulean City and head to Route 9. This route is well known for being quite obnoxious, long and boring, but it's not that bad. Just remember to stock up on healing items before entering. In the middle of the route, the TM for Aerial Ace is hiding in an item ball. It'd be a good idea to get it. Once you've made it out, you will find yourself on Route 10, where there is a Pokemon Center. This means you don't have to keep going back to Cerulean City to heal.
Blue: Pidgey (45%), Rattata (30%), Sandshrew (25%)
FireRed: Rattata (40%), Spearow (35%), Ekans (25%)
LeafGreen: Rattata (40%), Spearow (35%), Sandshrew (25%)