Assuming good faith is a cornerstone of the How I Met Your Mother Wiki. It is the belief that all contributions made by a user—be it an edit, a comment, or a Discussion post—are made with good intentions.
Assume good faith
This does not mean that users need to ignore obvious evidence to the contrary (clear vandalism and spam) or that discussion and constructive criticism cannot take place. Assuming good faith means users should not attribute the actions being criticized to malice unless there is specific evidence of malice. Everyone, but especially new users, should be given the benefit of the doubt.
Demonstrate good faith
In addition to assuming good faith, lead by example. The most obvious way to do this is by communicating clearly and make that extra effort to leave a new user an encouraging post on their Message Wall, explaining in more detail why their actions have been undone and give them tips to improve and thus prevent that from happening again.
When a user leaves a message that can be interpreted in multiple ways, do not assume they meant to attack you. When in doubt, politely ask for clarification. Remember that users from all over the world frequent How I Met Your Mother Wiki, and some things may quite literally get lost in translation.
Be sure to treat others how you would want to be treated yourself. We are all real people here, so treat them as you would someone in person.
Be patient with new users. Fandom has over hundreds of thousand of wikis, and a lot of them with their own set of rules and customs. While new users are encouraged to immediately familiarize them with How I Met Your Mother Wiki policies and customs, it may take them a while to truly grasp the wiki's culture and rules. Unless obvious evidence stating otherwise, a new user's misbehaving should be attributed to unawareness or misunderstanding of How I Met Your Mother Wiki culture rather than a conscious decision to not adhere to local policies. Everyone has the potential to grow into a valuable contributor. Take the time to guide and help them, rather than condemn and oust them on first mistakes.
Keep an open mind. It is also not uncommon for a new user to question a particular wiki practice they may not be familiar with. In order for a wiki to keep growing, it is important to keep an open mind to these suggestions, as sometimes a pair of fresh eyes may be able to immediately spot a flaw in the system that more seasoned users have glossed over due to being accustomed to it. Do not feel attacked and default to a "and who are you to bring this up?"-attitude.
Likewise, new users needs to be open to advice of more veteran users of the community. When an edit has been undone, assume that it was for a good reason rather than a personal attack or dismissal of your desire to help. When in doubt, reach out to the person in question and ask for clarification in a calm and polite manner. Misunderstandings happen. Communication is key.