Shih poos are very intelligent dogs and can be taught tricks and housebreaking fairly quickly, but it requires a regular pattern.
First, you will want to crate train your shih poo. This can be done by getting them a cage and putting her (or him) in at night when it's bed time. Also put her in if you will be gone in the day for a long period of time. If the crate is very large, you will want to block off part of it to make it small. Put a small round puppy bed in there to make her more comfortable. You will want to keep this area small to prevent it from peeing/pooping. It will not want to make a mess in the area that it sleeps in.
When you get home/wake up, you will want to take your shih poo out in the yard until it uses the potty. Use positive reinforcement- praising them or giving them a small treat after they do their business. Always get excited when they go outside so that they know they are doing something good. If she won't go right away, take her back inside for a little bit and try again. You will have to take your puppy out often while they are young.
When running around inside the house, watch your puppy close. If the shih poo is starting to make a mess indoors, pick her up right away and take her outside. Be very serious with her until she finishes using the potty outside. Don't yell at her when she makes a mistake indoors, you don't want her to associate the outside with punishment.
Remember to have patience and consistency. Eventually they will catch on but for some dogs it takes longer than others. Get a pattern and stick to it. Leaving them in a crate may seem cruel, but it's only while they are a puppy. Once they learn, you won't need to keep them locked up.