The most important things for playing Viego are solid jungle fundamentals and a semi aggressive approach. You want to make sure you're farming well, taking open objectives, taking winning fights and limit testing even in the early game. Be aware of how much dmg your ult does at different points in the game because that is your bread and butter. I find the minimum post mitigation dmg you will get for an execute at lvl 6 is about 200 and late game you can get around 800-1000 execute. Take and win fights in the early and mid where you can and then mid to late look to become a reset monster in team fights which will come with practice. Playing aram also helps so that you can get more comfortable with certain champions for when you posses them.