You'll want to give instructions to your top laner and make sure they are willing to follow through with your plan. You'll tell them something like "The two of us will invade their top side jungle, you take the buff but leave the small ones for me. If we get spotted we should abort." The reason for taking the small monsters for yourself is for the gold more than the XP. If the enemy top laner is smart, they'll inform the enemy jungler. After this you can either wait a short moment for the nearest scuttle to spawn so you can reach full HP again or you can move to your gromp/krugs, smite them and then carry on with your clear.

The enemy jungler has two usual options after you take their top side buff and a rare third:
1. They'll finish their bottom side buff and head into your jungle to take your bottom side buff. This is the "Hah! Now you're behind!" Although it doesn't bother Nunu much.
2. They'll finish their clears and when they get to top side they attempt a gank on top (You'll want to inform your top laner to be prepared) This is the "frustration gank"
3. They'll clear what they can and then head back to base simply cutting their losses. This is the "I don't want to risk losing more time"

After you've secured both your buffs or at the least, taken one and ensured the other is still alive you should turn your attention to the scuttle crabs and of course your other camps. Clearing scuttle crab is exceptionally fast considering your consume will do more than a smite can and has a lower CD. Once you've cleared your jungle or most of it, don't be afraid to enter the enemy jungler's starting side and stealing their gromp/raptor.