Asides from the obvious "only using your starter" thing almost everyone did in their first game (Bulbasaur in Blue for me), I also dumped a Pidgey in the Cerulean daycare the first time I went past it and didn't pick it up again until the E4 (level 52, iirc) and never realised dual-types existed until GSC. In fact for years I thought that dual-types were a new feature introduced in gen II and that everything was monotyped in gen I.