The first tip
First of all, it is important to decide on what technique you want to create a portrait, whether you will draw from life or using your imagination (and possibly a photo of the model).
For example, the American artist Joseph Lee works in the genre of abstraction, applying bold large strokes. His portraits are emotional but lack detailed. And the Spanish pastel painter Vicente Romero Redondo, on the contrary, creates emphatically realistic portraits, similar to photographs. Therefore, the desired technique will depend on how you create the portrait.