The one single thing that can kill a new forum before it gets off the ground is trying to make money up front.
Would you join a new forum packed with ads and pop ups with few or no posts?
Avoiding monetizing a new forum is typically a good rule of thumb. It takes time to establish and generate enough content in a new forum to reach critical mass or tipping point.
Ads or Hard Selling products makes sense when the forum has thousands of posts and registered users.
The number one reason you do not want to advertise on a brand new forum is really simple...
You want to keep users on your site for as long as possible instead of sending them off to a competitors site in exchange for a few cents.
Think about it, a popular form of revenue is using Google's AdSense that dynamically displays advertisements on your site. In my experience an average payout on the low end is the between half a cent to maybe five cents.
So if you stop to think how hard you've worked to generate traffic and get people to your forum to only send them away in exchange for pennies it just doesn't make sense.
If the goal of creating a new forum is to help sell products then let's keep that between you and I for now. Even if the forum is an extension of your existing site remember the goal is to generate valuable user generated content to draw in more search traffic and targeted leads!
The hard sell of your product should take place on your main site and not on your forum.
Putting up banners, pop ups or messaging users about your products can be a huge turnoff to new members who could find value in your forum, trust your brand and LATER buy your product.
To clarify hard selling is not the same as branding your forum. Do take the time to make your forum look as close to the design of your main site as possible. Branding is an important part if you're using your forum as an extension to your existing site.
This maybe the first time users become aware of your product or brand.
A new forum should have one goal, that goal is to build as much quality content as possible in the shortest amount of time.
The ideal situation would be if this content was generated by your forum users. The easiest and simplest way to enable users to post is providing an uncluttered path and instructions on how to contribute.
If the first thing new forum visitors see is a pop up ad, banners and/or links to advertisements it is more likely that you'll lose new users before they can make a contribution to your forum.
Here are two sections that should be in a new forum:
Introduce Yourself - It's a great way for new registered users to share a bit about themselves, their talents and what they hope to contribute or learn from the new forum.
By welcoming each user in your forum, you create a sense of belonging and secondly it creates a trend for the community. As time goes by the goal would be for established members to welcome new members on their own.
General Conversation (aka. Off Topic) - Another simple method of motivating users to post early on is giving a bit of liberty to talk about unrelated topics.
You may need to watch this forum little closer to prevent people from posting spam or competitive links.
Post rules early on to avoid shameless self promotion of competitors products. Rules also help with establishing what is expected from forum users.