Make sure the theatre curtain tracks or pole is installed. Usually looking up is sufficient to see, but you may need to climb up on a ladder if they are too high up to see clearly.
Decide whether the curtain you are hanging needs hooks, clips or ties. Usually theatre curtains have grommets (metal-lined holes) or clips.
If the curtain is going on a track and has grommets, it needs S-hooks to clip the curtain to the track. Hook one side of the S-hook into the grommet hole and tape it to the curtain with masking tape to hold it there. If the curtain is going on a pole and has grommets, it needs twill ties that get put on later.
If the curtain has clips, it has to go on a track. Measure the length of the curtain with a measuring tape and divide it by the number of clips. The resulting number is how many inches apart you place the clips on the curtain. Arrange the clips accordingly.
Set up a ladder that allows you to easily reach the track. Start at either stage left (the actor's left when facing the audience) or stage right and work your way to the other side of the stage. If the curtain is hanging on a pole, check to see if you can lower the pole to waist level. The pole is usually operated by a switch that lowers and raises the pole. This is easier and safer then climbing up to the pole on a ladder.
Hold the appropriate end of the curtain for the side of the stage you start on. For some curtains it doesn't matter because the front and back are exactly alike. Climb up the ladder and place the first curtain hook or clip into the first eyelet on the track. Continue in this manner until you reach the other side.
Bring twill ties with you if there is a pole. Tie each grommet hole to the pole using a double knot. The string goes through the grommet home and over the top of the pole. Continue to the other side of the stage as in Step 4.