Estimate your variance (i.e. how normal you are)
Most what we know is about averages. General wisodm, as well as modern learned science.
The value of the above depends on the average + your deviation from the average. there is a randmo component in this. But everyone is different in how unusual he is (how much variance to expect). the less usual the person the less vaue of common knowledge, and more on other methods of learning (personal experience, or other forms of educarted guesses. Accepting lack of knowlwdge i.e. acting with knowing that you do not know).
Practicaly, estimate how your are usual of different in various areas.
Correct for bias! Since we tend to see ourselves as more unusual than we really are, you have to adjust your estimate by adding the usual error in this estimate... (on average people thing they are lss average than they really are. We tend to be nomre usual than we subjectively perceive). I wanted to add that some people can somehow guess more realistically. But this would make every reader thinking he is of this kind.
Daniel Gilbert ("Stumbling on Happiness") offers that we should learn from others (from the outside you can perceive emotional results more accurately) and surrogate decisions to others (they are not involved emotionally and biased). He claims - with interesting data - that people are more similar than we subjectively judge.Surrogating decisions and learning from others, builds on the common between people and is not good for differences. The usefulness of it is crucially dependent on how average you are. The less average - the less use you get from studying average folks.
If you are truly far from average, remember:
1) Learn from weired persons. Stories of unusual folks may be much more relevant for your personal life than than average stuff. Either personal - get to know. or via books etc. The weired the better.
2) Tolstoy says that all happy families are happy alike, but every unhappy family is unhappy in its own way. Not to make the weired unhappy, but every weired paerson can be weired in his own way.There are still similarities between many weired people, and between subclasses of them.
Good luck in the fascinating jungle of the weired!