Take the dog outside frequently, especially after waking up, eating, drinking, and playing
Use the same outdoor potty spot every time
Reward the dog immediately after it pees outside
Supervise the dog closely indoors
Confine the dog when you cannot watch it
Clean indoor accidents with an enzymatic cleaner
Do not punish the dog after accidents
Establish a consistent feeding schedule
Limit water before bedtime if appropriate
Take the dog out right before bed and first thing in the morning
Watch for signs the dog needs to go out
Crate train properly if using a crate
Rule out medical issues with a veterinarian
Spay or neuter if marking is the issue and your vet recommends it
Reduce stress and changes in routine
Block access to previously soiled areas
Keep a potty training log if needed