Main goal of a website is, of course, to help the owner to increase sales and earnings. When you think about a new website (both if it is yours or if it is of one of your customers) sales and conversions must always be on your mind. Only when you have clear in your mind your goal, you can have a web site which reflects exactly what you need.
When you are developing a web site keep in mind that most if your users are not experts in this sectors. That said, a web site must be easy to use and must go straight to the point: if a user is looking for tips, a website must give to him/her those tips, if a user wants to buy something then he/she should complete transactions within few clicks (no more than 3 or 4 please).
When you have your amazing website ready is the time to promote it search engines and/or social networks (Facebook, Twitter, Google Plus, etc). If you have a website but no visitors, it will be absolutely useless. Online promotion is, for that reason, very important and can be put on the same degree of importance of web design.
Do not forget to have ready a mobile optimized version of your website. Traffic from tablets and smartphones increase day by day. On the average, today, one on five users visit a website using a mobile device, can you allow to lose all those potential customers? Of course not, so please do not forget to mobile optimize your website if you want to increase at top your online sales.