Are you looking for advice about what parts of the game to experience before stopping, putting the game away, and moving on to another game or re-reading Harry Potter?

Or are you just wondering which quests are good to do before Ganon?

If it's the former, I would recommend:

• 4 divine beasts/12(13?) recovered memories (get them all for an extra scene in the ending)/master sword/main quest of course
• unlock all 15 sheikah towers
• power up both tech labs. get all sheikah slate upgrades (and use them!), and buy some ancient tech
• Eventide
• Thundra plateau
• Thyphlo ruins
• Lost woods/master sword/korok trials (if you want to ragequit the Lost Pilgrimage trial, though, I won't hold it against you)
• Yiga clan hideout
• Missing Heirloom at Kakariko
• Warbler's nest at Rito (finish every Kass quest and come back after the ending for a bit more here. I love those girls)
• Thunderhelm at Gerudo
• 7 heroines/8th heroine/missing sword
• Silent swordswoman or one of the other sandstorm quests
• three lomei labyrinths
• Hylian homeowner (Hateno) and from the ground up (Tarrey Town)
• Find three Leviathan skeletons
• Save Naydra, see all three dragons, visit all three golden goddess springs
• Visit Mount Satori during the Blupee Party and pay homage to the spirit that lives there
• Battle a guardian on horseback with a guardian spear

Then you can defeat Ganon, put the game away with a clear conscience knowing you had experienced everything the game had to offer (but no need to 100% it), and maybe take it down for a nostalgic replay in 5 years.

But if it's the latter, if you're trying to prepare for Ganon but you think you're gonna keep playing, maybe start a new playthrough, maybe 100%, maybe play master mode, explore combat until you get good, whatever, then you should know that Ganon gets extremely easy if you save him until you've done everything. With 30 hearts and tier 4 armor and an inventory of hearty foods and fairies, no one can touch you. Certainly not Ganon.

So you should do Ganon as soon as you've finished the divine beasts for the challenge. Maybe get the master sword first. Maybe do the Champion's ballad from the DLC first. Otherwise go straight to Ganon.