As per usual when making automated tests I use "Inspect"(CTRL+SHIFT+I) in Chrome to find element by xpath, id, CSS selector etc. For example:
//li/a
Another option is to go to console section and evaluate your xpath like this $x("yourXpath") and hit enter. In the case of google search button woulb be like this: $x("//*[@name='q']") then you hit enter and expand the structure that appears below and if you hover with the mouse, the element is going to be highlighted.