Shulk is not the kind of character you can afford to autopilot if you want to play him well, in all honesty. His frame data is too slow to allow for much of that plus you have to be on point with your resource management of monado arts. Knowing when to use them in neutral, advantage and disadvantage takes time, and you want to avoid staying in arts too long and getting reversal'd or not having a particular art available to you (like jump art, speed art or shield art) in bad situations where you need to get out of disadvantage safely. Shulk's a fantastic character with quite possibly the highest skill ceiling in the game, but you have to be looking at the long term to achieve good results with him and do the character justice.
You can always join the shulk discord server if you're not a member there already, they may be able to give you better and more specific advice on how to minimize autopiloting with him. I would recommend just getting familiar with his game plan and focusing on the different elements of that throughout matches if you're interesting in learning Shulk more deeply in the meantime though, which the Shulk cord can also help you with along the way as well. Hope some of this helped!
