Value Betting Guidelines

[FourNickel]

Hi,

I am confused on when to value bet. I play 50nl 6max, agianst loose passive opponents. It "seems" that everytime I try to value bet they have just called me down with a better hand that they choose not to bet or check raise me with a monster. Or when I dont value bet and just check on a dangerous board I get shown a lower kicker. This is extremely frustrating. What are some guideline to value bet in NL, can anyone point me to a thread? Also, what fraction of the pot is a good amount to value bet on the last card? For whatever it is worth I used to play limit holdem and value bet relentlessly but things are different in NL when I can get check raised for my entire stack, since I am usually the aggressor.