Blue side:Your hope when clearing bluie side is that the enemy jungler does not go for bottom scuttler. If you can take bottom scuttler undetected, you get both a really good pink ward placement and a strong gank bot-lane. If the enemy jungler is bot, look for ganks or just keep clearing camps.
One good options after red is krugs->raptors->gank mid->top scuttle->clear blue side.
It is rarely worth it to contest scuttle, as zac is really weak 1v1 early.

Red side:When doing red side, you can look for ganks around step 4, 6 and 8. If the enemy team pushes hard you can sneak in a gank over the wall after step 2. Just remember that you need about 6 camps to reach lvl 4, which is when E has enough range for decent ganks.

First buy: Skip potions, not necessary on zac. Do these 3 camps as described below, then back and get Dark Seal.

Kill the 3 blue side camps:
0. Place your ward to spot invades.
1. Start at wolves instead of the buff
2. Pull blue and bromp simultaneously: Basic attack Blue, then walk towards gromp. Use Q on gromps as soon as in range, then basic attack blue once it's inside the Q range indicator. Kill both and use smite to survive.
Watch the video below if you're unsure:

Walkthrough of first clear:
Play Video

Bonus: why vision control is so important
Play Video