I'm sure there are a lot of different trainers in your area that offer drop in conformation classes....perhaps google it for your area and find one. I personally start my pups on Happy Feet by 8-10 weeks of age. By 3-4 months mine are stacking pretty decently....and then we begin to work on freestacking and holding a stack and holding while baiting etc. My 7 month old right now is doing great with stacking. We practice EACH and EVERY NIGHT for between 3-5 minutes and then I take her off her show collar to let her go be a bratty pup for the rest of the night
But there are also so many other things that you can ONLY get by attending a conformation class which is teaching your youngster how to act in a ring environment with other dogs around. A lot of youngsters want to play with their leashes, or bound and leap or chase other dogs in front of them, or get flustered that there is another dog moving behind them. You can't get any of that by merely practicing stacking at home. That is why we do both ~~ so that my youngsters learn to stack AND move in a group setting!!!
Best of luck....you'll find showing rather addictive once you start
Heather Peters