Different surface conditions require different braking techniques, and you’ll want to use your front brakes gingerly when traction is iffy. Locking up the fronts can easily cause you to lose control of your bike, while locking up the rear is much more likely to be inconsequential. The possibility of sliding either end of your bike will be greatly dependent on the traction conditions beneath your tires.
Enter areas where oil spills are likely with caution; these high-risk areas include intersections and parking lots. Drag your rear brake where you suspect slick surfaces, and you’ll have a backup plan in case you start to feel the front tires slide. It takes quick reflexes, so stay on your guard and remember that it’s much easier to recover from a rear wheel lockup than it is a front slide.
Those rules get taken to another level when it comes to riding offroad, as dirt bike riding almost never involves the front brakes. If you plan on hitting trails, make it a habit to keep your hand off the front brake lever, or else you might have to get used to tasting dirt more often than you need to.