For sensitivity, go on duel, dont fight anyone, just move your mouse around. Feel your movement and your swings. You have to feel like your mouse movement is completely in harmony with the swing, almost to the point where you can imagine the mouse is the sword itself. Then you will have found the perfect sensitivity. For me, it is at around 60% max. sensitivity.
To keep up between your view and block direction: Keep your hand steady. Try not to make sudden movements, it will blur your vision and you'll get lost. The technique is to move the mouse smoothly, and then a sudden movement in the right direction for the block. Sudden, but short. this will allow you to have the angle of vision you want and be able to block at the same time.
To be better in general: As others have said: Training, training and more training. Start by blocking the bot in single player tutorial. then move on to native. Once you are on CRPG,unlike other people, I would recommend having a full strength build and heavy armor for duel: The pace will be slower, because you will not respond as fast as the opponent wants, so the swings/response won't be as overwhelming ( be careful not to be spammed though). You will be able to make a few mistakes, and you can be sure that if you hit, you hit hard, and that's the fun bit. Nothing like seeing a guy fall, holding his bloody face between his hands. Trust me
Wrong block directions: Can be because of ping or simply because you failed your block. Many times I thought I blocked in the right direction. I was wrong. Train a bit more, then see how it goes. If it is the ping, well...you'll have to have a deeper look into your connection.
Slow to block/respond:
I don't see really what you mean here. It could be weapon stun, bad ping, or simply that you don't respond as fast as needed. Many possibilities, need details.
Hope it helps !