You can pretty much always go aggressive as soon as you hit Level 3. There's very few matchups he will lose this early especially if you take Ignite. If you get an early advantage you can basically always go in and even 2vs1 their Top and Jungler. Try to get your Tiamat as soon as possible and after that you can decide if you want to go tanky first or rush Titanic Hydra .

If your team is ahead you should Split Push, with your ultimate you can basically always get to your team in case a teamfight breaks out. If your team is behind you should stay with your team and try to get picks.

During late game teamfights you have to decide what you want to do depending on you team comp. If your ADC has enough peel you can go dive their backline and try to kill the enemy teams ADC. But if your team has no peel at all stay next to your ADC and protect him.