The fastest way to ruin great photos is a clashing outfit. Pick your shoot and setting — get a coordinated palette, per-person guidance, and what to avoid.
Coordinate, don't match. Matching outfits (everyone in a white shirt and jeans) reads dated and flat. Instead, pick a palette of 2–3 colours plus neutrals, and let each person wear a different mix from it. You get unity without looking like a uniform.
The other 90%: dress for the location (earth tones in a forest, soft pastels on a beach), avoid tiny busy patterns and big logos that distract from faces, and add layers and texture — a cardigan, a scarf, a knit — because texture photographs richer than flat solids.
Outfit sorted? The other half of a great photo is knowing what to do once you're in front of the camera. Use the free Pose Idea Generator for specific directions, or browse the posing guides for your shoot type.