how to set worksheet to fill in cells in suquencial order

I have a worksheet I am using for estimates. I want users to fill in all unlocked cells (formatted to be light yellow to indicate it needs to be filled out) and not be able to skip around and only fill out a small portion. I have used the "check" function but this doesn't always work. I still want some fields to be able to be left blank. Is this a feature in conditional formatting? I want to be able to tab from unlocked cell to unlocked cell in a certain order and when one cell is filled it will automatically jump to the next blank field. Some of these fields will be typed in and others have drop down boxes. I know that is probably a wrench in the works... I'm sure there is a name for this function but I couldn't come up with it. Any help is appreciated.