Edit in JSFiddle

var form = document.querySelector("#myForm"),
    elements = form.elements,
    total = elements.length,
    button = document.querySelector("#myButton");

button.addEventListener("click", function(){
    for (var i = 0; i < total; i++){
        elements[i].value = "";
        elements[i].innerHTML = "";
    }
}, false);

<form id = "myForm">
    <div>
	    Input 1: <input type = "text" value = "foo" />
    </div>
    <div>
        Input 2: <input type = "text" value = "bar" />
    </div>
    <div>
	    Select: 
        <select>
            <option>Hola</option>
            <option>Mundo</option>
	    </select>
    </div>
</form>
<button id = "myButton">Limpiar</button>