Rules for myself:
1) Learn from "the crowd" but don't feel obligated to emulate them. What's "hot" may not be what really speaks to you. On the other hand, there's probably a good reason why that company or figure is hot, so give it thoughtful consideration, but do follow your own heart at the end of the day.
2) If you come into a clear or unpainted version of a figure, track down a painted version as well for compliment and contrast.
3) Eschew flippers on eBay or elsewhere whenever possible. If someone is asking for outrageously inflated prices for something, especially something released within the past year, be patient and try to find it here or elsewhere for a more reasonable price. Supporting the worst of the flippers encourages them to keep doing their thing, and serves as notice to other flippers that what you (over)paid is "market value." Sometimes it's better to just cut your losses than to contibute to the perversion of a very cool but somewhat vulnerable collector's scene.
4) Unless you have a generous kaiju budget, primarily pursue one company or figure or colorway for awhile. This will yield a more focussed and hopefully individualized collection. (A personal preference. Some people prefer to have very diverse collections and there's obviously nothing wrong with that.)
5) Feel free to break rule 4 on impulse if something really jumps out at you and says "take me home!"
6) Practice the same good ethics and fair consideration in pursuit, trade, and sales that you would like shown to you. Your general "golden rule."
7) Do not talk to your toys when anyone's looking or is within earshot. Um, not that I ever talk to my toys. Not me!
