By giving their families and friends a genuine chance at participating in this country's economy.
And no, I don't mean "amnesty". Rewarding people that have already been in this country illegally is the worst incentive.
I'd replace it with a guest worker program, that gives them a chance to do what they really want: earn some money and send it back home. There's nothing wrong with that.
But, for citizenship, they have to go through the same process as everyone else: apply for permanent residency and 7 years later, they can apply for citizenship. No preferential treatment for permanent residency.
Assess a flat income tax on the guest workers, but don't call it Social Security -- because they won't be entitled to any benefits. And, the federal government rescinds all benefits for guest workers: no free health care, no free education, no welfare, etc. They are welcome to work here, but not to become a ward of the federal government. If a state government wishes to provide benefits, that's their choice -- but without federal money.
We will still have the problem with "anchor babies", and that can't be solved without a Constitutional amendment. Yes, I know that some people think it can, but the precedent has already been set and that's impossible to unwind.
Sounds good, but will never happen. The culture of many mexicans is almost as bad as most blacks. that we need to cut off all soccialized spending for immigrants, period, is a great incentive, but we have millions of illegals who have a taste for it.