I love the points that you made in this article.

So many new forum owners fall into these mistakes and then wonder why they aren't achieving as much activity as they had expected or wanted. It's challenging to be a community leader, or a leader in general but it can be extremely rewarding when things are coming along and going as hoped and planned. It just takes a bit more awareness and research.
Now going off the article and expressing my thoughts/opinions to the key points.
Choosing an Over-Saturated Site Topic
A lot of people make the mistake of having a forum genre that MANY other people have. What will you do specifically to stand out from the crowd and make people want to join your forum vs. the many other options that they have.
Sometimes it can be good to have a forum topic that is popular or well-known as it may be a bit easier to get some members at first, however whether or not they become a loyal long-term member is another thing.
Making Too Many Categories and Forums
Many forum owners want to make sure that there community covers everything, and that's okay. There is a way to do that where the forum doesn't feel cluttered or over-whelming. Maybe get some sub-categories or make the forums a little more general and less specific. People can be turned off by overwhelming them with too many options. Sometimes having a bit more narrow of options is a good thing. Plus it can also help your forum seem a bit more active.
Waiting For Posts To Come Rolling In
I see this time and time again where forum owners spend lots of time and effort setting up their forums and as soon as they launch their forum they expect it to be the next hot thing and people are going to be signing up to their community like it's a free all you can eat buffet. But unfortunately that is rarely ever the truth. It takes time and consistency for you to build a community and an active spot. Usually when a restaurant opens it's doors for the first time they don't have a constant flow of customers walking in the doors. It's something that the business owners need to promote, they need to upsell etc. With forums it's important that even though the forum may not be as active as the forum owner would like it, they should still post and keep things up to date. You want people to want to come and join, register and be a part of the fun, they don't want to see that no one has posted in the last 2 weeks. It may be a struggle at first but it's all about promoting your community so people know about and then making the members experience amazing so they want to keep coming back.
Too Many Chiefs, No Indians
Unfortunately, I see this WAY too often in newer forum communities. It's good that you want to have staff members and people to help you run your forum and community but having too many staff can actually hinder your community. Think of a grocery store, I'm sure they have managers & workers, but do they have more managers/workers than customers? No, because that wouldn't make any sense. When setting up a forum don't make the mistake of over staffing because not only can it be overwhelming to new members but it can make your forum look less active because only staff are posting on a regular.
Heavy Promotion and General Begging
Promoting your business, community or forum is always a good thing but there is such thing as being pushing and over promoting. There is a place and time and as a forum owner you need to figure out when those times are and how you're going to promote. Are you going to post on social media, are you going to make posters, are you going to post on other forums etc.
Neglecting Mobile Responsiveness
Most people have phones and generally use them more than their laptops so it's crucial that you not only have a mobile friendly forum but that the experience on the forum through the phone is just as good as if they were on their laptiop.
Neglecting User Engagement and Community Building
As a forum owner it is up to you to set the standards on what you want for your community and that means that you have to be engaged and know what's going on with your members, staff and forum. Again, think of your community as you would a restaurant owner, you don't just create a restaurant and then sit back and let everyone else do everything. Of course, you need to delegate some tasks and it's good that you don't do EVERYTHING especially when the community is booming and active. BUT you also have to be present and engage with the members. Not only will it help increase posts/threads but members will want to support a forum owner that they know (or get to know from around the forum) then an absent forum owner they know nothing about.
Allowing Spam and Inappropriate Content
By allowing this you are telling your members and potential members that you have no standards and no control. That this is a free for all and no one is held accountable. It's a horrible thing to do because it shows laziness and incompetence.
Neglecting Regular Updates and Maintenance
Once more, think of your forum like a restaurant. If you don't do the maintenance and updates on the vats, ovens, tables, chairs, staff etc. your place will eventually fall a part and people won't want to come by anymore because it's no longer what they are looking for in a restaurant. Keeping it up to date lets members know that you are still active on the forum even if you aren't able to post as much as you'd like. It also lets members know that you find your community worthy of updating and maintenance and that you care about your community. If a community is out of date and things aren't working correctly people aren't going to want to join and the members won't want to continue to log on. Instead give them a good reason to come back regularly and grow with the community.
Conclusion
I know I didn't touch all the topics that the article had, however these are just the topics that I had something to add. Thanks again
@Cedric for this amazing article.