All Members should read this deeply so you will know how you can put the negative and positive reputation. Not just like "clicking" the +/- just like feel like clicking it.
What are good and bad things to give positive reputation for?
Reputation should be given to people who post meaningful, helpful, and thoughtful posts. Any post that contributes to the thread in a positive way probably deserves positive reputation. This does not mean that you agree with what was said; the point brought up may be completely opposite to what you believe, but it may be a good point nonetheless, and worthy of a reputation point. Giving positive reputation to someone because they are your friend and deserve to have a few more rep points next to their avatar probably isn't a good reason to give positive reputation.
What are good and bad things to give negative reputation for?
Negative reputation should be given if the person is posting something that detracts from the conversation. If the post is rude, inappropriate, breaks forum rules, is not gracious, etc; these are all good reasons to give negative reputation. If you have a personal grudge with someone it is not appropriate to give them negative reputation for no reason. Giving negative reputation because you don't agree with what was said is not an appropraite use of the reputation system. People are entitled to their own opinions, and just because you don't agree doesn't mean the user was wrong or not contributing to the conversation.