Please don't get me wrong here, for I am trying not to be facetious, but what you are asking, books have been written about - the basics of photography.
I would suggest that you got one and read it.
However, someone on the forum the other day used the term ' a balancing act for aperture, shutter speed and film (camera) speed and I liked that term.
To put it simply....
Most lenses work best stopped down a couple of stops.
The more any lens is stopped down, the greater the depth of field. No matter how much a lens is stopped down there is only one point of perfect focus and depth of field gives an area of acceptable focus. Telephoto lenses have much shorter depth of field than wide angle.
Try not to use a shutter speed slower than the reciprocal of the apparent focal length of the lens ie at 60mm focal length, try to not go slower than 1/60th sec.
If you got away with an eigth of a second, you did just that, got away with it, unless......
You were using flash when the flash, perhaps 1/1000 of a sec or faster, made the exposure anyway and, again within reason, the camera shutter speed was irrelevant anyway.
The answer, use f5.6 if there isn't enough light to use f8 !
I wrote this message and then looked at your profile. You have some great photos on the database already and I find it hard to believe that someone who takes such good photos (and has great equipment) could not understand these basics.
If this was a flame, I've fallen for it, if not it is just indicative of how much easier things are today.
Mick Bajcar.....over forty years as a photographer and still learning to balance