All too often my design company, Ciplex, is faced with individuals who have thought about their site and know they need something. They come with firm ideas as to how they want their site to look--but they haven’t even thought through the basics.

That’s why I always ask this first: “Why do you need a site?,” not “What do you want on it?”

Websites are marketing tools. For many businesses, it’s the only source of business. If done right, it can be a major part of yours.

Here’s my list of the top do’s and don’ts when building your site:

Do: Set smart goals. Ensure they’re measurable. Here are a few great ones a Web designer wants to hear: increase conversion rates, increase sales, generate more leads, reduce overhead, and improve brand awareness.

Become an SEO wiz. Search engine optimization is something you need to know about even if you plan to hire someone to handle it. SEO is great because it can put your marketing on autopilot, allowing you to focus on your business instead of bringing customers to click on your site. Start reading SEOmoz and stay up to date with SEO changes by reading sites like Search Engine Land.

Use open source tools. You could go with a proprietary content management system (CMS) but then you’ll be stuck with one company, paying big license fees. Try an open-source system—like WordPress or Magento—that any developer can access.

Think about mobile. What percentage of your visitors are coming to your site from mobile devices? Is it high? Consider building a mobile site or an app.

Steal from competitors. Check out your competitors and see what they’re doing well. If you like the look and feel of their site, use it as inspiration and make it your own.

Develop content. If you’re going to sell products on your site, get product photos and product descriptions ready. If you sell services, describe each one. Save weeks by getting as much content as possible together before designing.

Write with calls to action in mind. Having a big sale? Don’t just write a banner that says “50% off all products.” Write one that says “50% off all products, CLICK HERE to view.”

Always answer “why?” If you want people to do something on your site, like sign up for a newsletter, don’t just put up a box that says “enter email” or even “sign up for newsletter”—you’ll get a very weak conversion rate. Tell them why: “Sign up for our newsletter to receive weekly specials.” Same thing for Twitter and Facebook. Tell people why they should follow you--what will they get out of it?

Trust the Web designer. The worst results come from an “I know what I want, just do what I tell you” attitude. You hired an expert--let them do what they do best.

Don’t: DIY. Your website is where your customers first experience your brand. If it looks homemade, they may make assumptions you want to avoid.

Make people think. Do a three-second test: If within three seconds a visitor can’t figure out what to do next, go back to square one.

Expect visitors. Lose the “if you build it, they will come” mentality.

Spend all your money. You can make a well-designed site for under $1,000 from a freelancer, or a few thousand dollars from a professional agency.

Add a blog. Are you really going to write posts? Be honest. If you won’t, then forget about a blog. An outdated blog can create the perception that your company is small or even out of business.

Add Twitter and Facebook buttons. If a potential client clicks through to your social pages and sees hardly any followers, they may lose trust in you. Build up your social presence by posting and engaging your fans on a regular basis, and only then promote them on your website.

Try to please everyone. Figure out who is likely to be your most frequent users and focus on creating the best experience for them.

Add testimonials. Too often testimonials appear or read as fake. “’They are great!’ says John Smith” simply isn’t believable. Make sure testimonials are specific and relatable.

Use Flash. Adobe just announced that it will no longer support Flash on mobile devices and set-top-boxes. Make sure all potential customers can access your site.

Expect a killer website overnight. Good websites take time to build. If you want the best results out of your site, be prepared for several months of work.