Perhaps one of the biggest reasons so many people are unsuccessful at getting their websites ranking well is that they believe everything they read on the Internet. Think about that logically for a minute: if SEO information was readily available to everyone on the Internet, then everyone would be in competition with everyone, and there wouldn't be a need for SEO experts.
This is why it really bothers me when someone asks for my help then doesn't want me to do my job because they "read online that it doesn't work". Well, guess what? I know what I'm doing! That's why you hired me!
So how do you learn what SEO tactics work, and what ones don't? It's easy...the most effective way is to join an exclusive SEO community such as SEO Book. Aaron Wall has incredibly valuable information, and offers many tools to help you with your SEO quest.
Web Marketing Now and SEO Revolution are 2 more great resources for useful and effective SEO tactic information.
Trial and error are options; in fact, that's how a lot of us find out what works and what doesn't.
If you don't want to take the time for the learning curve, hire someone who knows what they're doing to do it for you. This is great for those who want quick results to improve their business.
Just remember that about 99% of information freely available on the Internet about SEO is bogus.