selenium-Webdriver

I am new to use Selenium and I have problem about locating a dynamic element. Could you please help me? Thank you very much in advance.
Here is my situation:
i have the following code to enter username which is dynamic so I cannot use its fixed id. Is there any way to locate it correctly?

"input id="_jsx_0_3l" class="jsx30textbox" type="text" label="username_txt"/"



but i have tried with this

//input[starts-with(@id,',_jsx_0_')]

but it did not work
please help me on this
please help on this

You can use class / type to locate that text box

Code:

xpath=(//input[@type='text'])
//input[@type='text']
xpath=(//*[@class="jsx30textbox"])
//input[contains(@id, '_jsx_0_')]

thanks it worked fine

which one you have used?

I used this : //input[@type='text']