I have a line chart for months. I don't have any value for July and that is getting skipped. how to ensure July over there?

This is our default Behavior, Tableau follows while creating the report when you don't have data for some specific or date. That particular month will be escaped while developing the report in such cases. If you are looking to sort that month also where you don't have any that I have labeled all you have to do is click on the month dimension and check the option called “show missing values”. This will allow Tableau to pick up those months also where you don't have any records available in your data set.