Some people navigate through pages using the tab key rather than the mouse. Specifying a tab order allows these users to access items in a logical order rather than the order specified in the source code.
Default tab order follows the order that links or form elements are coded in the HTML:
Try to ensure that the default tab order is the most logical route
If you can't, change the tab order to suit user needs, using the tabindex attribute:
Most suitable for forms
Follows numeric order lowest to highest (use positive integers)
Tip: Use the keyboard to tab through the page. Does it make sense this way?
Examples
Second <input ... tabindex="20">
First <input ...
tabindex="10">
Third <input ... tabindex="30">