- If a plant isn't genetically hard-wired to produce jumbo pitchers, then its not going to make "lose-your-slippers-in-it" sized pitcher no matter what you do. Some plants are genetically coded to produce their largest, best pitchers only when they have reached a certain stage in their life cycle, so in some cases, that will mean waiting years for pitchers like the ones Sam and Geoff and Rob sometimes show photos of. Growing Nepenthes is a waiting game, in case you haven't noticed. You can't rush success.
- optimize the growing conditions! You know what Nepenthes like, so the question is, how close to ideal are your growing conditions? Many growers don't have the option to provide perfect conditions, because they are limited by their living situation or budgetary limitations, and so they have to opt for "as close as I can get", and when you compromise on some of the key factors, the results will be a compromise also.
Provide as much light as is optimal for the particular species/hybrid. Not every species likes full sun exposure, but some love it. Not every species thrives in shady conditions, but some demand it. Study, ask questions and make an effort to engineer the best site for each individual plant. As Geoff has intimated, there is no "secret recipe" for monster pitchers. You can't just fertilize a plant with everything you can find and expect horse-sized pitchers, all of the small details add up to have a significant impact. If you compromise on temperatures, light quality, humidity, soil quality, and nutrient availability, the results are going to be less than ideal.