The people would be chosen using stratified random selection from everyone on the electoral roll. Here are more details:
Every two years a large number of randomly chosen citizens (around 10,000 people, selected from the electoral roll) would receive an invitation asking if they are interested in learning more about serving in the House of Citizens.
All expenses would be covered (including childcare, lost wages etc) for those interested to attend an information day, located at various large cities around the country, where the details of serving in the House of Citizens would be explained and their questions answered.
Those interested in serving would give a few details: age, gender, home address and educational level attained. This is used to ensure that the random selection produces a group of people that match the latest census data - to ensure that it is a representative House of Citizens.
Finally a stratified random sample is selected from those willing, ensuring that as people are rotated in and out of the House of Citizens it remains gender balanced with a proportional number of people across all age groups and education levels, matching the latest census data.
For more details you can wait our forthcoming detailed proposal, or see the similar proposal put forward for a Citizens' Assembly in the Scottish Parliament.