Preventing backlash, no need to time your thumb on the spool....A lot of it comes from.
Not overfilling the spool...it will vary from reel to reel as well as type of line used. But you should leave 1/8 to 1/4 inch from spool lip.
Properly setting up the spool tension. You want the spool to stop when your lure hits water. Or touches the ground if you are inside your house doing the precheck before fishing. I like to setup against a 3/8 oz. weight.
Brake setting, it just depends on lure type or windy conditions. It works in conjunction with the spool tension. It can be set up where there would be no need to even thumb the spool.
Even making sure your levelwind line guide is centered before casting is a huge deal.