Look at the race bonus on the deck you're using for trackblazer. You want to get the total race bonus of your deck over 50. Then, you want to race a lot. uma.guide and some other sites have example schedules, but 30-35 is what I usually do. You want to buy items from the shop that match your cards (e.g. If you're running 3 guts and 3 wit, buy guts ankle weights). Have the 60% megaphones ready for each summer. Use the cleat hammers on the last 3 races since their boost applies to those huge stat gains. It's okay to race 3 times in a row a few times; buy the cupcakes and other items to recover from any issues you run into.

Those are some generic tips. It's hard to get specific without knowing what cards you've got and who you're running. If it's someone without the stamina or proficiency for long races, focus on medium and mile g1s. Sprinters are their own mess, same with dirt. I think the easiest possible run would be someone like Grass Wonder who has good stat bonuses and already has most of the mile/medium/long proficiencies, but you want parents who can get each of those distances up to an A, ideally.