I am not the best at teaching stuff but i can assure you you can learn stuff from here

At the start of the game it is best to ward river near your buff to avoid any invades and remember to ask your bot and supp to leash until the buff is about 800 hp so you can smite and last hit the buff with your q then just take all your camps then try to find an opportunity for a gank

When ganking remember to do this "W-E-Ghost-Q-Bonk-Profit"
Then try to invade the enemy jungler's jungle if you cant invade try to take down a tower using your ult and q

When going for dragon, baron, or rift herald remember to get there first if the enemy team gets there before you it will be hard to retake the area
if you succesfully secure obj then if needed use your ult to take the objective quickly

As nasus jungle you should not focus on kills only focus on objectives and tower if you try to get more kills to increase your kda their is a possibility that you just feed the enemy team and become useless lategame so try to splitpush more often

Mid game you basically try to secure objectives and towers and try not to give enemy free farm also tell your team to play safe until you can run the enemy team down and basically kill them all play safe until about 400-600 stacks this is the safest amount of stacks from my experience since it is enough damage to 3 hit the enemy adc with enough items

When you and your team is behind in gold you should focus on farming more and stacking up since whatever happens early game doesnt matter if you can scale till late game

Try to force the enemy damage dealer into split fights so you dont have to worry about the damage dealers team and you can secure a kill more safe

When splitpushing remember to check the map so you wouldnt be stopped by the enemy team
you can also splitpush when the enemy is taking an objective and you know that you cannot steal because you are a bit behind focus on towers because destroying the nexus wins you the game not getting kills

remember to buy bloodthirster or other lifesteal items when you see that your sustain is not enough buy something like deaths dance maybe even spirit visage to boost your passive lifesteal

Your main focus as a jungle nasus should be taking towers objectives and stacking up your q remember to not thirst for kills you need to focus more on smiting the objective rather than focusing on champs when you are at obj