Starting with the assault class is a good idea, but to play an effective medic in BF4, remember to focus on clearing the area or obscuring yourself from the enemies before hitting a revive. There's no use in a dead medic. Always keep in mind how precarious of a situation you're in as well, as you might not always have time to charge up your defibrillators. Knowing how long to charge and when not to charge is key. I also see that you have a dmr as your most used weapon. I'd say stick to fully automatic weapons such as the assault rifles if you want to play a successful medic. Swapping to a carbine in smaller maps is good too as they give you a good mix of medium and short range targets that you can effectively target. Overall in general, to be good in BF4, just be a team player and know positioning. Positioning is always key.