In photography, the bigger the light source and the closer it is to your subject, the softer it is. You might argue that the sun is huge, however, because of its distance the sun is a harsh source of light. This is why during an overcast weather, the clouds represent a natural light diffuser.
Your flash / speedlite has the same problem. Because it is a very small source of light, if you point it directly at your subject, the result would be a harsh unnatural photo with ugly shadows everywhere. We need to disperse those light rays from directly hitting our subject. To do that we use umbrellas, softboxes, and diffuse panels in studios. What to do though if you are shooting on location, you only have one speedlite attached to your camera hot-shoe and you want to make the best out of it.
Bounce the flash off the ceiling at 45 degree angle and use the palm of your hand to reflect some of that light back onto your subject. Without the white card on your speedlite or your hand for that matter, shadows will cast under your subject's eyes and nose. You subject should be 1 to 2 meters away from you for this techniques to work. If done properly, the ceiling will act as your main light and your flash hand as your fill light.
Bouncing light off the ceiling without the hand thing will manifest some shadows as we saw in 1 above. Therefore, why not mimic a big softbox to the right or left of your subject. Try a white wall and swivel your flash at 45 degrees to hit that wall and bounce back at your subject. If you add a reflector symmetrically at the opposite side, you will have your fill light.
Bounce the flash at the corner of your ceiling and wall. Meaning target your flash behind your head pointing at the 90 degree intersection of the white wall and ceiling. This will mimic the source of light coming from a diffused sun. Let your subject hold a reflector just beneath their chin so that fill light open up the shadows beneath their nose and eyes.
If you are stuck in a situation where there are no white walls and ceilings available or they are extremely high to be able to bounce that light, use a flash-top diffuser like diffuser domes, omni-bounce, Lambency flash diffuser, or a 15 cm softbox fixed by velcro on the flash head.