Pressing the clutch first before applying brakes is a big no no.
Because if the clutch is pressed first, the engine drive to the wheels get disengaged and the brakes have to work really hard to halt the vehicle. Needless to say it will increase your stopping distance also which is always risky.
So it is advisable to apply brakes first to allow the car to decelerate with the help of "engine-braking" and the apply the clutch when it is about to knock or stall.
Not to worry, you will master this art by practicing just like all other experienced drivers.
Braking at crawling speeds is a different story altogether and here you can press the clutch first and apply brakes to avoid stalling the car which is already moving too slow. Even if you apply the clutch first here it is safe at this speed because the momentum gained by the car after pressing the clutch is comparitively much lesser than that of highway speeds and it is easily controllable by the brakes with a lesser wear.
Hope this helps.....