ok well,to beat the first trainer i recomend that you have a a good electric pokemon like zapdos and a fire pokemon,for the second and the third trainers get a good psychic pokemon,and for the forth,get a pokemon that learned ice beam,that will help alot,and for gary get an electric pokemon and a flying pokemon.
hope i helped
i found a few errors. zapdos is part flying and ice beats flying. so i recomend a fighting type (machamp) or an electric type (electrode,riachu, etc) for the 1st. as for the 2nd i say get a water type. it will help alot. also get a flying attack in it for the fighting type. as for the next, go with physcic (alakazam/kadabra) and for the last, dragon or ice. for dragon i say dragonite. if you wwant an ice. i might have to say dewgong,lapras, or articuno. then you have the champ. i forgot his pokemon sadly