I play a lot of Jungle Naut myself. Clear is super easy if you know what you're doing.
Flat armor seals, Magic Pen Marks (you can use attack speed marks as well, I don't), and Flat (or scaling) AP Glyphs and Quints is my usual setup.
Start shield, and use it 5 seconds before Gromp spawns, you'll get the full usefulness of the shield by the time he pops it and it will be that much closer to being off CD for blue buff. After Blue buff you'll be around 3/4th health, you can gank mid or go straight to red buff then Skuttle then bot/mid then go back.
Few things you can do for the build. Standard you'll want to go Mobis or Mercs/Tabi, Cinderhulk with either Trailblazer or Stalkers, Rod of Ages is great as it solves his mana problems then just build tanky healthy items. Righteous Glory is a nice buy.
Alternatively something I enjoy doing is Runeglaive on him. Clears camps insanely fast and makes him CC chain train chunk people down when you weave your spells together with your empowered AAs. Try it out sometime! Though not in ranked. You'll get yelled at.
Skill wise is matchup dependant. If you think you can gank a lot then max riptide, if you think you'll be behind and need to farm your jungle, max shield. You might also want to consider putting an early second point into hook. Reduce the CD a bit to something more reasonable. Not super worth it but hey, it's an option.