Here are a few tips and ideas you should consider before starting a website or forum. A lot of these tips are more common sense than actual web insight, but they're overlooked and need reiteration nonetheless.
One of my biggest pet peeves in forum creation is that most people go into it alone. If you can help it, please avoid doing this. There are probably successful boards that have been started by one person, but it's inadvisable to start a project by yourself. Always have someone who has similar ethics and interests help you out, but make sure you trust them. Trust is a tricky thing on the internet; you can't really tell people's motivations that well, but trust them enough to count on them to not do anything stupid. All too often I hear of people stealing websites, defacing their site, and backstabbing others in an effort to take over. Know the person you're doing business with since, in many ways, making a forum is similar to a business. Plus, think of it as another person to help you build content on your site. You're effectively doubling your chances of creating a successful page by doing so.
Conversely, it doesn't usually hurt to be a bit untrustworthy of people at first if you're running a website (not to say you should be paranoid at all). Point being, don't go around giving people you're not fully acquainted with access to the admin panel, FTP, or cPanel. In my few years of administrating forums, there was only one other person I trusted enough to have unrestricted ACP/FTP/cPanel access on my sites. That's obviously an extreme, but my point is that giving access to your site's administrative structure opens you and the site up for bad times. People's intentions are not always good.
Perhaps the biggest aspect of site creation is having your own niche in the online community. Being "just another gaming site" is fine if that's all you're aiming to be, but for most people that isn't going to cut it. Find something that interests you and that you won't mind writing about or talking about or getting sick of. Making a broad, all-encompassing discussion forum is probably not a good idea simply because there's a near infinite amount of them already. It helps to narrow your specialization and really force content in that given area. For example, instead of making a music forum, make it genre- or artist-exclusive (IE make a forum for a band or style of music). Also, don't make a site just for the sake of making a site. Make one because you want to and because you have knowledge you want to share. In many ways, you're making the website for yourself, not for others.
Another HUGE issue is that people aren't familiar with the software they're using before starting a forum. Not pointing any fingers or calling anybody out, but if you're going to start a website, the least you could do is educate yourself on the software you're using. The vast majority of support threads could be avoided completely if people would familiarize themselves with their software and the various add-ons they're using before opening a site to the public. I highly recommend opening a test site and simply perusing it until you're comfortable with the majority of the settings and shortcuts. That's not to say you have to have mastered HTML and CSS (though it definitely wouldn't hurt), but simply knowing where settings groups are and how to change basic options is enough most of the time. Starting a board without knowing how to edit simple details like the board title is frowned upon.
Building off my last point, have a clear image in mind for your site before creating it. Think of color schemes, logo ideas, font choices, and so on to create an identity to help your site stand out amongst the countless others out there. From a designer's standpoint, branding is one of the most important aspects of creating a website or forum. It's important that your site has its own image and identity to prevent it from being grouped in with all the other sites in it's category. I highly highly highly recommend using custom skins, but not everyone is proficient in coding languages or has a near endless supply of money at their disposal so it's obviously not a necessity. In my line of thinking, every detail says something about your site whether it's the colors of your usergroups or the layout itself. Is that to say that having oddly colored usergroups will make your site less desirable? Probably not. I'm just really anal about little details. However, these "little details" add up. Having a website that looks awful is almost as bad as having a website with no content, but I digress.
All too often I see people rushing when they make their forum. Research your competition before making plans. Ask yourself, what are they doing right? More importantly, what are they doing wrong that I could improve upon? What do they lack that would benefit me? Why did they choose this layout? Could I make it better? That being said, don't blatantly copy another website. My point is that you should learn from what others have done before you in order to avoid repeating history, in a sense. A little bit of knowledge goes a long way.
Advertising your site can be a bit tricky. There's several ways to build hype for your site, but my general rule is don't advertise on other forums. For example, going on Se7enSins advertising your gaming forum is a really stupid idea because 1) you're usually making a fool of yourself and your site, and 2) nobody's going to join. If you wouldn't want somebody advertising on your site, what makes you think other people want you doing it on theirs? It helps to have a group of people that you're a part of that will help you out and spread the word, but not everybody has that luxury. Social networking and SEO are both invaluable tools in advertising and building hype. Several years ago when I started a digital art forum, I went on art networking sites (namely deviantART), made an account under the site's name, then began "watching" (synonymous to "liking" or "following") other artists who I deemed to be a good addition to my site when it opened. I uploaded relevant artwork and created a few blog/journal posts regarding the website and from it I ended up gaining a few thousand members in a very short period of time. Not everyone will have that luck (if you can call it that), but my point remains. I'll likely end up writing another guide about advertising since there's a giant laundry list of tips and tricks that are fairly useful.
It's important to be patient after you've created and opened your board. As many have said before, your website isn't automatically going to flourish; you need to put time and effort into it and, with a bit of luck, that'll go a long way. If your site isn't popular in the first few weeks or months, don't sweat it. Everything takes time. It's amazing how many websites start out, then launch a V2 update a week later. Be patient. It's a virtue.
Lastly, keep calm. If something on your site is happening or it's not turning out how you wanted it to, that's okay. Remember: THIS IS THE INTERNET. If your website with five members got corrupted and you have to start over, it's not the end of the world. On a somewhat relevant side note, if your "urgent" support question on here regarding your brand new website with 13 total posts isn't answered immediately, you'll live.