When you start the game, you should start with Bulbasaur, it will easily take on the first two Gyms alone with its Vine Whip
This is a glitch similar to the tweaking glitch in D/P that allows you to 'sneak' past the champion and enter the Hall of Fame. Here's how to do it:
This glitch takes advantage of the fact that in this game, you can switch the slots of items as well as Pokemon. To do it, you need two items, the second being Oak's Parcel. Open the bag, press Select on Oak's Parcel, then hit Cancel twice and return to the field. Now start a wild battle and select the Pokemon menu, then attempt to swap the first Pokemon. To prevent the game from crashing, the Fight menu must be opened. Defeat the Pokemon using the normal methods.
You have now triggered the glitch. Now walk 83 steps, landing the final step in front of the door of your rival's house. Enter the house. You will warp to Route 7. Now go to Celadon and enter the Pokemon Center, then immediately leave. Now walk left until the Dept. Store blocks your way, then enter through the right entrance. You will warp to Lance's room in the Pokemon League. Walk through the door. Now try and walk past Blue. You will be in the Hall of Fame, which will trigger the credits.
An alternative method would be following the above steps, but instead of entering the Pokemon Center, you should enter the Condominiums, immediately exit, then enter the Dept. Store. This automatically warps you to the Hall of Fame, although with glitchy graphics.
If you evolve your starter Pokemon before receiving your Pokedex from Oak, the game will assume, because you have two Pokemon registered as 'caught' that you already have a Pokedex, and not allow you to continue, no matter how many times you give the parcel to Oak.