Where to start with immigration?
The biggest problem with immigration is that we have a bunch of socialized programs that use the force of law to steal from one class of person and award it to another class for having less. If my legally liable tax burden increases for every poor dumb fucker in the country, then it's only a matter of time before the average person figures out that being a dumb fuck means a lot of free time to fuck around without a care in the world while others address the practical concerns of existing. Which invariably leads to … well - what has been happening. Complete economic evaporation and collapse.
Throwing immigrants into the mix just adds a whole new excuse as to why people shouldn't be responsible for feeding their own damned face. Get rid of the notion that existence warrants the use of force by government to sustain individuals at the cost of others… and much of the immigration issue fixes itself. A return to real money would also help quite a bit.
Otherwise, the border need be secure for the purposes of public health and security. The only other real gripe is the need for citizens to be the only ones who vote, and for each citizen to hold the Constitution's due process as a sacred virtue to be adhered to above any other governing virtue (laws aren't about what a judge feels is 'fair' - nor is government about whatever 'wins elections' - the process of government must be understood and held sacred by each citizen).
But this is speaking in mostly ideal terms. Practicality would still argue for controls on the number of immigrants/refugees and a screening for talents.