Cross check all 'undocumented immigrants' receiving government benefits with voter registration roles. All those who have committed felony elections fraud should have all government assistance ended immediately. If they are working their employer should be notified that his daily fines will also begin immediately.
(My guess it that the subsequent self deportation would be rapid and significant.)
STEP TWO:
Take all illegals serving time in federal prisons, state prisons and county jails, transfer them to labor camps along the southern border and put them to work building the wall. When they are done release them on the other side.
I like the work camp idea. Good one.