Welcome to PC, right well firstly be great by providing some context. What type of rock are you sculpting? because they've unique characteristics much like fingerprints, dependent upon climatic conditions and/or region/s they're endemic too or indeed how they were initially formed....etc
"I struggled a lot trying to get a rocky silhouette and understand how to use the common blender brushes for this kind of sculpt." Visual Language may help, in creating a more rock-like textured silhouette and as for your finesse with Blender's default sculpt brushes, then imo you've actually nothing to worry about really,…