Early game, try to harass the enemy laners from a safe distance with tormented soil. This will build up your gold income from spellthief's and poke the enemy down while healing you slightly from your passive. If you get a chance, snare the enemy with a dark binding as long as you aren't too low on mana. Try to keep your mana pool at least halfway full unless you are doing really well. The reasoning is that morgana is a pick champion more than anything else, so saving enough mana for a full rotation of spells in case of a gank from either side is wise. If you get a good chance to push the lane with your adc, go ahead and use your pool on the minions to help with that push. Be very careful of ganks though, as you will be vulnerable if you push too far.

Try to keep a fresh set of wards in the river and in the lane bush if necessary. This will allow you to scout for ganks and roams as well as allowing you to get picks on the enemy. All of these things can help you and your jungler take control of dragon, or stop it from happening sometimes. The river is a great place for you to fight since your ult will force the enemy to scatter. If your teammates are nearby, don't be afraid to fight in the river.

Late game, you have a couple pretty important jobs. One, peel for your adc or mid laner, which ever one is getting focused in teamfights. Black shield and bind can be a great way to keep them alive, and if they dive your backline, just press ult. Be wary that the enemy may try to focus you while you are ulting, so don't forget about Zhonya's, because your ult will complete even if you zhonyas. You can be a good bait. Also, if the enemy team is grouped up close together, you can flash in, ult on several of them, and Zhonya's when it is necessary. This can be a great way to initiate a fight, and can win teamfights by itself if you and your team are positioned correctly. Don't forget to continue to ward, this can be a great way to catch someone out of position or make a good rotation if the enemy team is out of position.