A concrete practice-tool routine for Zac, built around its real cooldowns and ability costs.
Each time Zac hits an enemy with an ability, he sheds a chunk of himself that can be reabsorbed to restore Health. Upon taking fatal damage, Zac splits into 4 bloblets that attempt to recombine. If any bloblets remain, he will revive with an amount of Health depending on the Health of the surviving bloblets. Each bloblet has a percentage of Zac's maximum Health, Armor and Magic Resistance. This ability has a 5 minute cooldown.
Do nothing else for five minutes. The passive is the piece nobody isolates, and it is the only part of the kit that is always available.

Each time Zac hits an enemy with an ability, he sheds a chunk of himself that can be reabsorbed to restore Health. Upon taking fatal damage, Zac splits into 4 bloblets that attempt to recombine. If any bloblets remain, he will revive with an amount of Health depending on the Health of the surviving bloblets. Each bloblet has a percentage of Zac's maximum Health, Armor and Magic Resistance. This ability has a 5 minute cooldown.
Zac stretches an arm, grabbing an enemy. Attacking a different enemy will cause him to throw both targets towards each other.
Zac explodes outward towards nearby enemies, dealing a percentage of their maximum health as magic damage.
Zac attaches his arms to the ground and stretches back, launching himself forward.
Zac bounces four times, knocking up enemies hit and slowing them.
Practice tool lets you reset cooldowns, which is useful for learning a combo and useless for learning a champion. Turn the reset off and cast on the real timings — knowing what an ability's downtime feels like is most of what separates a comfortable champion from a new one.
Zac runs on no resource at all, so the only thing rationing abilities is cooldowns.
Unglamorous, and the highest-value five minutes of the routine. Melee champions have completely different tower-farming patterns, and this is where you find out which one you are actually playing.
These are the designers' words, not ours — the tips shipped in the client for Zac.