planets ruling difficult houses in the chart

1
hi there,

i am not sure how to formulate this question, but it has to do with planets that rule over the 6/12/8 houses playing a more negative role in the chart.. it is a very general idea but as i understand it indian astrology has some rules connected to this, or general ideas in association with this.. the reason i ask is i have seen the transit of a planet into a different sign bring changes when nothing else explains the change.. hopefully this makes sense and someone can offer some places to for me to start reading about.. thanks.