Do you have a specific model you would like advice on?
Smooth shading can give quite good effects with relatively few polys!
Also, modern devices can actually handle tons of polys now, so lowpoly is becoming less and less vital to a game, especially on PC You can see @chamferzone guns are made for games like Call of Duty, and can be 6k faces for a pistol alone... (for mobile it's still best to keep it as low as possible)
One of the 'tricks' although it's not easy to learn, is to have a good topology, meaning the polys should follow the main shapes of your model, that allow both smooth shading, lowpoly, and good animation. The best thing to learn is to see all the amazing things on sketchfab with wireframe on to see how it's done, and practice!
Here are some models you can check out, toggle wireframe on to see how they manadge smooth shapes with low/med polys (good texture painting helps alot!):
hand painted lamp
Parasaurolophus Walk Cycles
Hope that helps a little ^^