If your photos look flat, the answer is almost always lighting. Get this right and everything else gets easier.
Natural light (the gold standard)
A north-facing window between 9am and 3pm gives soft, even, diffused light. No shadows, no colour cast, no work required. If you only have one light source for the rest of your life, pick this one.
Golden hour
30 minutes before sunset, low and warm. Beautiful for outdoor shots, dramatic for indoor shots. Move fast — the window is short.
Ring lights
Cheap, even, foolproof. The downside: the circular catchlight on shiny surfaces (polish, skin) is a dead giveaway. Diffuse with a sheer white cloth to fix.
Softbox
A small 40cm softbox at 45° above the foot is the pro setup. Even, directional, with controllable shadows. Pair with a $20 reflector on the opposite side and you've matched a $2,000 studio setup.
The $30 setup that wins
A white bed sheet taped over a window during midday. Done. We've seen 9.5-rated photos shot this way.