My mini security camaras don't get a good signal. Is there any tricks or
Signal boosting devices I can try

If they have a detachable antenna you can upgrade to a better directional antenna. If they are in one direction you can get a better antenna on your receive side as well.

I experimented with my system (purchased at Sam's, not a professionally installed system). I ended up placing the small receiver/monitor in a central location reducing the distance to the individual wireless cameras (or maybe I should say- equalizing the distance to the cameras). I then run cable from the receiver/monitor to tv's which I use for actual monitoring from more than one location. This works well for me but if you want to use the small receiver/monitor that usually comes with these units as your only monitor, my method means that you may not be able to have that monitor located exactly where you want it. And once cable is plugged into those small monitors, the screen on the small monitor goes black so you have to do your monitoring on the TV (s). But I have one output from the small monitor going out to 3 TV's and there is plenty of power to handle that. Just depends on how you want to do your monitoring.