First of all, congrats on your choice of plant because Cacti are true survivors!
They have tough skin and spiky bits so bugs have a hard time doing any damage. I find this is also great for plant burglars that take a liking to my plants on my front verandah!
The easiest and most common way of killing cacti is by overwatering.
Dont forget that these plants originate from arid areas so can survive without much water. Do let them dry out between waterings and feel the soil before you do add any water. If you feel any dampness in the soil dont add any more water or you will risk root rot.
Cacti like light, so wont do well in low light areas indoors. Cacti will survive indoors but prefer an area that receives good light, for example near a window or window sill. Of course they do well outside but if you have had your cacti indoors dont go putting it outside for a spell in the hot sun in summer. Like any plant, a sudden change of climate will not make your plant happy.