First trade with one of the people on Cinibar island then surf up and down the East coast wiht it until you come accross a Missingno. pokemon catch it and put it on top of the you're list of Pokemon then fly up to Viridian city and look at Missingno's stats then talk with the Old Man who shows you how to catch pokemon then fly back down toCinibar island and surf up and down the coast again and you should come across things like level 175 Charmeleons and level 160 Missingno's and sometimes level 0 ++m++ "Mysterio" but don't let any level 0 Pokemon in you're PC until it's level 1 at least.