I think I've run into situations alot recently where I know that if it folds to me then I should be raising the hand I'm dealt, but I'm never as sure when someone opens before me and I'm considering a call. I know that I need to be folding the worst hands in my range from a given position after someone enters the pot, but I'm not always sure how much tighter I should be playing.

For example, say it's a full ring cash game and I'm in the CO with K9o which I'm planning to raise if it folds to me but someone in MP opens with a standard sized raise. How much better would I want my hand to be to call the raise? Would you call if you had KTo instead? K9s? Or would you want something like ATs to call?

Anyone have a good rule of thumb or something?

This is where preflop charts come in handy. I would go with the following:

Ideally, we should have a plan to play a K9o post-flop. Calling K9o on a raise just in the hope of hitting a good flop is very bad.
For example, a flop comes that doesn't help us much, like A73r, and the villain bets on the flop. What action should we take in this scenario?
So, as PrinceJigger said above, it helps to have a defined range with which cards we will play in each position and how we will play them in different scenarios.

me personally i dont care much about the strength of my hand when i am in position . i will see the flop and then act

just find the chart of the starting hands on the preflop, and study it well. With K9o on CO, against a raiser, in large stacks in a full ring, it would be a bad idea to call, unless you have a plan for this villain and if you have the right board, you will bluff him