I don't recommend washing your braids or twists for at least 2 - 4 weeks after an install but that's just my opinion. I like for clients to give their hair time to break in, your hair needs to settle in or it will lose some of its luster. There are many ways to spruce up your box braids or twists but you should be well into your 2nd month before that even becomes an option in my opinion.
Now if your a person who works out alot , plays sports, naturally sweats heavily, just has a flaky scalp or if you just feel a need to wash sooner and or more often I encourage you to do what feels right. I never want my client to sacrifice their comfort for looks, you shouldn't even have to.
If and when you do wash your braids or twists please take into consideration that this is not your real hair and therefore I don't suggest you wash it like it is but of course you do have that option. There is a way to clean your hair and scalp without compromising the integrity or the longevity of the design. Especially since for most of us, our real hair has a tendency to expand after its been wet, It's best if you follow these steps when you wash your braids or twists.
Use luke warm water preferably in a shower, wet your hair and scalp. Then step out of flow of the water and proceed to add a small amount of shampoo and or conditioner and begin to work that into your scalp GENTLY using just your fingertips focussing ONLY on your scalp. Work the excess shampoo or condition down the length of your hair. And rinse thoroughly. Moisturize, moisturize, moisturize... Be sure to moisturize your hair with your favorite oils and allow it to air dry naturally for best results.
Do not get in there and go crazy at least not until you've had your braids in for a good amount of time. I do not recommend washing your protective style everyday. Maybe once every 2 weeks. On a regular day just tie it up and cover it when your in the shower or sleeping. A bun is also a nice alternative to keep out the extra moisture between washing. And get the most out of this style.
Limiting the use of products will help you to avoid dirt and build up. Keep it simple, take your time and be gentle . You don't want to age your style by adding unnecessary ware. At the end of the day I prefer my clients didn't wash their hair while it's in a protective style. But I want you all to know how to do it right should you ever need to.