As for hiding the lighting; whenever possible I try to get my main light coming from the same general direction as the ambient. Sometimes you can’t do that, and sometime the ambient IS the main light source. In any event, my first thought is always to
bounce the flash against a wall or other surface that is not visible in the photo. A speedlight is about 1” x 2”, which is essentially a “point” light source. It will create harsh light and hard-edged shadows. But if you turn it around and bounce it off the wall, even from a distance of a few inches, the light beam spreads out and you have an apparent light source of 12”, 18”, or even much more coming back into your scene. It’s like having a big softbox, and as a result you get much gentler light, and much softer shadows.
Here's an extreme example where I had to pump a LOT of light into a scene, yet it looks very soft:
And here's the setup:

This is taken from the viewpoint of the chair in the above photo. You can see that I've set up directional lighting, most of which comes straight in, but some from the far end of the room. And look at the size of the hotspots - those strobes are maybe 12" or 14" from the wall, tops. In effect, I have 3 jumbo softboxes working for me here.
If you have a large, unpartitioned space to light, and you’re working on a scene at one end, you can turn a speedlight around and fire it at full power at the far end of the space, just nuking that end of the room, and the effect is like having a twelve-foot softbox down there coming back and blanketing your set with perfect light. Then you can use additional lights in a very subtle way to sculpt the lighting around whatever effect you want. I might pop a flash in bare-bult at very low power (like 1/64th or less) just to create some edges or relief, but the main light source is that big explosion I created out of frame.
Bouncing lights is awesome – but you have to very clever about controlling the spill from the lights – the hotspots can be huge and it can be very frustrating at first. But after a while it gets kind of intuitive, where you can place lights and where you can’t. Tiny adjustments in height, angle, and power settings will translate to big differences in your photo. You have to experiment.