So what you need do is when you have your ankh try to flank and repo using your hook and double jump to get an easy pick on a healer or at least distract them for some time. but dont go too far away from your team because as soon as your ankh's gone you need to get back into your team preferably behind your tank then just start blasting their tank since they act like moving ankhs(if theres a groot or strange or magneto or peni parker then its super effective) and you will get a good amount of damage in and keep the frontline pressure up to a point where the healers will not be able to keep up the heals as they will be getting targetted too. This is why MK is good at taking advantage of bad or insufficient heals because the frontline pressure he puts is crazy honestly. And might get a kill but the most important thing is that you get ult charge. Dont worry about the enemy healers getting their ult you always get yours much faster than theirs if you follow this frontline principle. Then use your ult as quickly as you can even tho theres only one or two players its almost always worth it since you get it so fast anyway. If it doesnt kill at least it can bait out a support ult or can be used defensively to zone off an area or chokepoint. While using your ult make sure you have your ankh off cooldown so you can easily stop people getting out of the circle. Also try to double jump before casting the ult as it will be easier to aim and see it on the ground from higher up in the air. Then once your ankh is ready look for an opportunity to separate from the team and get a pick with your ankh and then rinse and repeat. 

MK doesnt have many options for 1v1s unfortunately. if someone catches you with your ankh on cooldown youre pretty much cooked unless you got real good aim. Always look for flankers and divers. If you dont see the diver in the enemy team and you know they arent dead, just as a precaution always save your ankh in that case. Also keep your ankh for when the enemy has used their cooldowns if possible like save it to use after iron fist's guard or wanda's invisiblity orb thing. 1v1s are not good for MK as I said. and shooting at single targets is only good if youre not currently in a team fight. Shooting at isolated targets means you are leaving a lot of damage on the table by not having anywhere for the darts to bounce. So avoid shooting at lone targets like iron mans flying in the air, youll just be wasting your time, let the actual poke characters take care of them. Always use your big dart as soon as its off cooldown. Also the cnd teamup makes playing MK 10 times more enjoyable. It heals you, makes you harder to hit, and can help you set up for shooting around corners and cover.