the difference is reflexive and not reflexive. Actually in the example that you provide there is no big difference.
If you do something for yourself is reflexive: Stehuju si
if you do something for somebody else is not reflexive: stehuju
I wash myself: myju se ( I do something to myself in general, without mentioning specific noun)
i wash my teeth: myju si zuby (I specified the noun)
I wash a car: myju auto (general, not reflexive usage)