Before you start applying for a US visa, it is important to differentiate between an E1 visa and an E2 visa. The E1 visa is applicable for foreigners who are Treaty Traders while the E2 visa is for Treaty Investors. The difference is that Treaty Traders conduct trade on behalf of a company or organization while Treaty Investors merely invest and operate enterprises in the US. Whichever of these 2 visas you get, you should be a citizen of a country that has binding treaties with the US to qualify for the E type of visa.
You may find E2 visa rejection cases to be quite many. For one, if you cannot prove that your country has a binding treaty for commerce and navigation with the US, you can expect your visa application to be rejected. You should show that you invested sufficient capital in the enterprise you will be operating in the US, meaning there is enough for the enterprise to do business and that you do not intend to withdraw the capital invested. The investment should be significant enough to be considered profitable and will generate enough income to sustain a livelihood for you and your dependents.
Some other reasons for E2 visa rejection are: if you fail to prove that you are an officer in executive or supervisory capacity of your enterprise; and if you are simply an ordinary worker for the enterprise (regardless of skill level.) You can avoid getting rejected by following US rules for visa application to the letter.