Gather balloons in your chosen colors and sizes
Get a balloon pump
Get balloon arch tape or a frame
Inflate the balloons to similar sizes
Tie off each balloon securely
Group balloons into pairs
Twist pairs together to make clusters of four
Attach the balloon clusters to the arch tape or frame
Fill gaps with smaller balloons
Adjust balloon placement for a full look
Secure the arch firmly in place
Trim any excess tape or ties