Wash your hands three times. Put a few coins in a tzeddaka box.
Putting your hands on the dough, say the blessing for separating challah (see image below).
Then, pull off a piece and hold it up in your right hand. Only this piece should now be in your hand. Directly after the blessing, say this text:
This piece is now your separated challah and must be disposed of correctly. It cannot be eaten or used.
Give yourself time to really pray at this special opportune moment. Add personal prayers as well for yourself, your family and dear ones.
One of the many prayers you may say at this time is the one below:
Here is a hafrasha card with tfilos with the text above of the bracha plus more special tefilos to say while doing the mitzva of separating challah.
After you have finished your hafrasha and prayers, leave the dough, covered by the plastic, to rise until doubled in bulk, about an hour or a bit more.
And then, enjoy! You are ready to shape!
May your home always be filled with the blessing of the Torah about challah:
להניח ברכה אל ביתך, (Yechezkail, 44:30)