There are a few factors that are important to consider when developing a Magento eCommerce site.
First, you need to make sure that your server meets the system requirements for running Magento. You can find the system requirements here: http://devdocs.magento.com/guides/m1x/system-requirements.html
Next, you need to choose the right version of Magento for your site. Magento has two different versions - Community Edition and Enterprise Edition. Community Edition is free to download and use, while Enterprise Edition is a paid version with more features and functionality. You can read more about the difference between the two versions here: http://www.cmtelecom.com/blog/deciding-between-magento-community-and-enterprise-editions/
Once you've chosen the right version of Magento, you need to select a hosting provider that meets the requirements for running Magento. You can find a list of recommended hosting providers here: http://www.magentocommerce.com/resources/websites
Finally, you need to choose a theme for your site. Magento has a wide selection of themes to choose from, or you can create your own custom theme. You can find a list of available themes here: http://www.magentocommerce.com/magento-connect/themes.html