Shulk relies on zoning you out with his Monado's range with aerials such as N-air, F-air, & B-air, & getting in some grabs while cycling Monado Arts to change up his game-play to help adapt to most MatchUps. My advice to you is to play Shulk first, get a feel of what all 5 of the Monado Arts do exactly, & go from there for starters. Mainly Shulk has trouble handling heavy projectile walls, & despite him having good range, he doesn't necessarily have fast-frame moves except for Jab & ofc grab; this means that when a character is in our zone, it's kinda hard for Shulk to handle any up-and-close aggression. He especially doesn't favor being combo'd either.
If you play someone like Sheik who can needle needle needle, then Shulk is forced to approach, usually putting on Speed mode is normal as an example. Sorry for not giving out specific characters other than Sheik but hope this helps.