Tacere means "to be quiet", not "to make quiet".
Unless you want to do something like "make it so that your mind is quiet", tacere is not an option.
One possibility in this direction is cura ut mens tua taceat, "take care that your mind becomes silent".
The verb tacere does work for "quiet yourself".
The simple order tace means "be quiet".
If you want to combine the two orders to a single maxim "quiet your mind and yourself", you might want to use two different verbs in Latin.
The verb quietare (or deponent quietari) seems to mean "to make quiet", but I was unable to find any classical attestations.
However, it is a very naturally derived word for this meaning, so I have nothing against using it unless you have a specific era or style you want to follow.
This appears to be a transitive verb, so you can make "your mind" into an accusative object.
The most suitable words for "mind" in this context seem to be mens, animus, and anima.
You can compare these words in a number of online Latin dictionaries.
If you want it to mean more "mind" than "soul", I recommend mens.
This brings me to the translation mentem tuam quieta, which is very literally "quiet your mind".
I would tweak this a little and use dative instead of a possessive pronoun (which plays the role of a genitive of ego here).
With dative it becomes more "quiet the mind for yourself"; it indicates that you will benefit from quieting your mind.
I like having the two orders together, and certain emphasis can be added by putting the imperatives at the ends.
My recommendation is this phrase (or a part thereof if you only want one at a time):
Tace et mentem tibi quieta.
Be silent and quiet your mind.
