Unreliable evidencePersonal beliefs rely on evidence. People draw evidence from sources varying in reliability. Good reasoning skills require evaluating reliability of sources.
What we learn first generally takes precedence. We learn first from our parents, associates and schools. Reasonable skepticism requires that these beliefs change in light of better evidence.
Anecdotal evidence tends to be accepted if it comes from a friend or trusted source. Such evidence should always be mistrusted. Even your own personal experiences are likely not as generalizable as you think.
Evidence from peers tends to be accepted, but its quality depends on knowledgability of the peers. If the peers are experts in the field in question trust may be warranted, but one should otherwise be skeptical.
To be accepted, evidence should be consistent with physical laws. Knowing the basics of physics, chemistry and biology is a great help. If your scientific knowledge is weak you should defer to experts or make special efforts to improve your understanding. Note that formal education is extremely valuable in this regard, but not essential. It's possible to familiarize oneself with science basics through reading and discussion.
In my experience most people are careless with evidence. They tend to accept opinions of peers and to prefer stories to documentation. They also tend to let emotion override reason.
Wikipedia generally provides reliable information, but as with any source, it's worthwhile to delve deeper than a single article so as to understand the information in a broader context.
Be aware that alternative medicine is usually quackery and that politicians are more interested in pleasing constituents than in conveying truth.