Liso vs. suave
While both liso and suave can be translated as "smooth" in English, they describe different qualities. Liso refers to the physical texture of a surface being flat and even, while suave refers to the sensation of something being soft, gentle, or mild.
Liso
A2This word describes a surface that is physically even, flat, and without bumps, wrinkles, or texture. It focuses on the topography of an object. It can also mean straight when referring to hair, or plain when referring to colors or patterns.
La pared debe estar perfectamente lisa antes de pintar.
(The wall must be perfectly smooth before painting.)
Ella tiene el pelo largo y liso.
(She has long, straight hair.)
Prefiero las camisas de colores lisos, sin estampados.
(I prefer plain colored shirts, without patterns.)
El hielo del lago formaba una superficie lisa y resbaladiza.
(The ice on the lake formed a smooth and slippery surface.)
Suave
A2This word describes a pleasant sensation, most often to the touch, meaning soft or gentle. It doesn't require a surface to be flat. Suave can also describe mild flavors, quiet sounds, gentle movements, or even a mellow personality.
La manta de cachemira es increíblemente suave.
(The cashmere blanket is incredibly soft.)
Este queso tiene un sabor muy suave y cremoso.
(This cheese has a very mild and creamy flavor.)
Hablaba con una voz suave para no despertar al bebé.
(He spoke in a soft voice so as not to wake the baby.)
La crema hidratante deja la piel muy suave.
(The moisturizing cream leaves the skin very soft.)
El avión realizó un aterrizaje muy suave.
(The plane made a very smooth landing.)
Summary
In short, use liso for things that are physically flat, even, or straight, like a table, a road, or hair. Use suave for things that feel soft or are gentle and mild, like a blanket, a flavor, or a sound. A silk scarf can be both lisa (flat) and suave (soft), but a fluffy wool sweater is suave but not liso.