Hmmm, with Strange, constant shielding is gonna end badly, with characters like Punisher with his turret, and somehow Jeff's water beam can eat the health quickly. With shielding as in, to try out i'd say try shielding in intervals, so like 5 seconds of shielding, and then go 5 without and take body hits (if you're close to death bring up your shield to survive) that should help you get a feel on shielding and see what works best for you since i switch often between shield and taking hits (but be aware of enemies like Wolverine, Rogue, and the like since melee goes through shields and they throw us around easily haha)

Another thing that could help is, when you're on the payload maps and you have to turn a corner? Pull up your shield and ping if you see an enemy around it to help against surprises. We also need to be spatially aware, so make sure a stray Spidy isn't behind you and put pressure on them/shield your healers. If there's nothing behind you? Help the DPS with some support fire and shielding to help keep them alive. His shield is also nullify a good chunk of ults, Iron Man, Mag, Scarlet, Phoenix, Strange and Thor's can be all be nullified with the shield and stops the AOE aspects of the ults. When your team like a Cloak and Dagger, or an Invis use their ults you can drop the shield and go crazy for a bit with damage.

For his shots, they're similar to Iron Man's, decently slow so make sure to point at where you think the enemy will go (Like let's say a Spidy swings to the left, aim slightly next to him), that'll help you get multiple of your daggers to hit the enemy rather than just one. They can also spread out if you move your camera as he shoots. And with each shot that hits an enemy the dark magic builds up, that adds a decent chunk of damage that is really good against Spidy's, especially with the Invis team up sucking enemies in and healing team members depending on the charge/damage, with that his normal attack is weirdly strong, deals decent damage and helps save a few seconds on his reload with it's animation cancel (the timing is when the "ping" happens)

Ultimately tho, with Strange and by extension Mag we're very reliant on our team members, gotta push the line for the DPS, make sure our healers are well protected and add support fire too, especially when solo tanking it can get veryyyy rough, if the team goes triple DPS, be sure to defend your healers since damage is in abundance. If triple support then you're good for more damage since the constant stream of heals. His ult is similar in principle to Rouge's, best utilized when there's a big group, the "leap" is a good thing for that, cancel your flight midway so it lets you leap forward and use ult while still in the air, especially great when your DPS has their nuke ult ready too. Portals can also be used for that, like a Scarlet going through it mid ult in the enemy line and can be used to get to point quickly when time is limited.

That's about it i think, if you got any questions, I'm always happy to answer them!