Strict immigration quality laws (as in, three strikes and you pay for your one way ticket home).
Fix police funding and then demand performance from them.
If there's a problematic area, put enough cops there so they pluck everybody undesirable one by one until the rest is benign and/or got the hint.
Control unemployment (we don't just want low numbers, rather evenly distributed), discourage walled settlements, try to mix people together.
Instead of providing welfare checks, make policemen/teacher jobs. Still can't find work? Try hard or get booted (if you're some kind of immigrant, of course).
The main take off is - it works until you break it. If you have a broken socity, stop complaining and fix it, it's absolutely doable.
guard-of-terra for Mayor!