Would one of the better methods to crack Bitcoin be to start creating a massive database of key pairs? It would then be possible to reference the Private key required off the public key from the DB.
It will take significant resources (probably more electricity than can be generated by all fossil fuels on Earth) and time (orders of magnitude greater than the age of the universe) to generate a complete Bitcoin address "rainbow table".
See these answers for more details.
You would hit the heat death of the universe before you came anywhere close to generating even a single already used key pair.
If you don't understand the math in the key pair generation you should take that as an indicator of the uncertain ground on which you tread.