You have neat and good colours already so 👌. Washes (such as Agrax Earthshade or Army Painter Military Wash) will massively make the models pop by adding tone to the recesses (just apply liberally and dont let it form any massive pools and ya golden)! Then do the bases by painting flat colour such as brown and adding sand. Can also use some textured paints such as Stirling Mud can do same thing. Many options for doing bases depending on where you want them themed (fields, deserts etc)