Joining a clan is a huge part of most massively-multiplayer games. They're called “social games” for a reason.
If you never join a clan, you'll miss out on lots of important advantages that clans provide: protection, extra resources, infrastructure, and camaraderie.
If you're determined to go it alone, you will find yourself easy prey for everyone else who has a whole clan to rely on!
That said, it's equally important to join a clan that you will actually enjoy being a part of. Being part of a clan where you don't fit in won't help you out very much, and might even discourage you from playing the game at all. Don't ruin your gaming experience by committing yourself to a group you aren't comfortable with.
Find out as much as possible about the clan you're considering joining. Check to see if they have a web site, an outlet on social media, an e-mail newsletter, or anything else you could look at to get an idea of what the clan is like.
If you aren't sure what the “clan culture” is like with your potential clan, ask! Message the clan leader and ask if they have any of the aforementioned resources to check out, or if they can personally tell you anything about how the clan operates. You should also check up on whether the clan has many enemies – you might not want to join a crew that's hated far and wide.
Joining a clan is a big decision, so make sure you make it an informed decision.
A simple but oft-overlooked factor when joining a clan is, “Where do they operate from?” If most of the clan members live in a different time-zone from you, or speak a different language, you might struggle to fit in. Try and get some idea of what days and times the clan is most active, and make sure you can fit that schedule, at least to some degree.
Besides that, find out what the culture of the group is like. Are they interested in friendly socialization among members, or are they serious and business-like? What kind of expectations do they place on members?
Will you be required to contribute troops and resources to clan endeavors, and if so, how much and how often? Are clan members mostly autonomous, or are you expected to follow orders and stick to a plan?
Knowing these sorts of things will help you get the most out of your clan experience.