(This is what I do.)
For the Sim itself:
Be optimistic, look for the good things about the sim or the assets you may be using.
If I have created something (I.E. a route, loco, etc.) take pride in the accomplishment and if I am not quite satisfied with what I have created then I fix it so I can be satisfied.
If I can't find anything you like about the sim or content, then I try to see what the it can become and perhaps make suggestions in the suggestion boxcar here on the forums.
For the Community:
Patience is key, not everyone has the same opinion, some folks may be new, and some I just have to force myself to be patient with.
Compliments, suggestions, and constructive criticism can go a long way...
Avoid asking for content or release dates. (I know that I have done this in the past but since then I have learned.)
Avoid insults, provocations, and being just plain rude. (I have been rude once before in the past however I apologized to the said person at whom my insult was directed at.)
If I have insulted someone, I apologize to them.
Thinking before I post.
Sometimes I just have to have "thick skin" and ignore some things.
If someone lacks wisdom, help them or explain to them whatever wisdom they are lacking.