You are opening up your aperture to f/1.8 or to f/2.8. Opening up the aperture means using a large-sized hole (apoerture) to admit light; thise larger holes are the low numbers, like f/1.8 or f/2, or f/2.8, so the correct term is opening up the lens. The larger-sized apertures are low in numerical value, like f/1.2, a very LARGE aperture, or f/1.4 or f/1.8. Small apertures are the apertures like f/8, or f/11, or f/16, which are tiny little holes, but which have high numerical values. Setting a small aperture is called stopping down the lens.
There really are NO specific "ideal" setttings for any situation; settings depend on the desired pictorial or creative effect; for example, if you want to show a guitarist's hand movements as a blurred hand, slow shutter speeds like 1/20 second or slower might be used. Same with drummers and stick movement: slower speeds like 1/90 second or 1/80 or 1/60 second will show some movement of the drumskin ends of the drumsticks, but the hands holding them will be mostly sharply-rendered.
ISO level can be set to AUTO ISO, and in Manual camera mode, the photographer can establish the desired/needed f/stop value (let's say f/4) and the deisred/needed shutter speed (let's say 1/125 second) and the camera will automatically adjust the ISO lvele upwardly or downwardly, to get the "right exposure" for the settings of 1/125 and f/4. ISO level used depends on the camera to a high degree, but also personal preference.
In general, with longer lenses (80mm,90mm,100mm,135mm uop to 200mm) shutter speeds of 1/100 second or faster are best for motion-stopping and limited camera shake and minimal blurring due to long lens lengths magnifying the image. With SHORT lenses...like 50mm and under, shutter speeds can be dropped lower,like into the 1/60 to 1/20 second range, with minimal blurring of subject movement due to the short lens having LOW magnification of moving objects.
On an overall stage shot, say one done with an 18mm lens from the wings....it might be possible to go as slow as 1/8 second, and make a decent frame of mostly-still people. A tight close-upo shot, say an at-the-microphone shot of a gyrating singer shot with a 200mm lens, that tight of a shot might easily require 1/160 second to get a crisp, non-blurred shot.
Again, there really are no "magic" nor any "ideal" settings, just as there really are no "magic" lyrics and no magical, one-size-fits-all singing method.