After all of the money and effort has paid off the visitor you wanted is now on your homepage looking at it... making decisions. There are tens or more likely hundreds of other sites the visitor can go to the question is will the customer stay on your site or leave and why?
The last thing you want is to have spent $3+ on a targeted ad click or even a free Google organic click and not have it pay off. Conversion is just another way of marketing. Now your marketing to someone who wants your product but the customer wants a very clear value proposition and to know that your product or service will work for them.
Your website is built to answer questions. Is your product or service in the customers price range? Are others are happy with it? Are a reputable person/company offering this service or product? How about what your product solves what is it and why should I spend money on it?
1. The shortest most clear text "Always Have a Clean Pool" or "Healthy Value Priced Bird Food"
2. Clear way to order
3. Phone number that doesn't go to voice-mail.
4. Video(s). People want to see it in action to better understand it.
5. Multiple Images, screen-captures = proof.
6. List of value propositions... how will this make the customer or save the customer money?
7. Customer Testimonials
8. Any awards, business associations, or anything that can prove you are a legitimate company.
Use a service like www.mturk.com to cheaply hire people to test your website for usability, post to your Facebook friends and ask if when they go to your website do they clearly know what your offering and how to order it? Be sure to ask people will give you their true opinions
Next test your site live with new customers. Spend $100 on Google Adwords and see if you have any results. Make a goal, for example you might need one sale for every 10 clicks or every 5 clicks. Be sure to look at your competitor websites and incorporate anything that you like from their designs in your own way to your website. Remember the main goal of your website is to make sales, if it isn't performing then your website needs further work.