I have a badly bruised toe. How do I treat it?

Assuming it is . Not broken, ice it. Avoid tight shoes and when walking lift up your foot rather than push off of it when you are propulsing.
Xray. You should get an xray to rule out a fracture if there was trauma involved. Ice and elevation of the foot will help with symptoms.
Refer to answer. Keep toe clean. Tape it to adjacent toe to keep it from moving too much. Most suspected bruised toes also are broken. To make sure see your dr.