Most breeches and jods will have a care tag inside. Always follow manufacturers directions.
If you have leather knee patches or leather full seat riding pants, use a laundry product made for leather like Pepede, or Leather Therapy Laundry Solution, they will help keep your leather soft and supple.
If your leather gets dry, try Leather Therapy Laundry Rinse and Dressing to keep those knee patches and full seats supple.
Some people think it is a good idea to wash your breeches inside out to resist fading. I would be careful if you have dark leather on your breeches. Always hand wash or use gentle cycle and cold water unless your care tag tells you differently. Do not dry clean. Turn breeches right side out and immediately hang to dry to reduce bleeding of any dark leather into the fabric. You can roll them in a towel before hanging to get out excess water and reduce drying time A teaspoon of white vinegar in your first wash water can help set the dye in the leather.
Many breeches are now coming with silicone knee patches or full seats. These can be washed and hung to dry without the fear of the silicone losing its grippy feel.
White breeches? Try some Scotch Guard to help keep them clean on show day. Follow directions on can, do not spray on leather.