If when you are currently filtering on one (or more) Tag, I suggest that whenever you create new task (using Tab+N) that the new task is automatically given that Tag(s).
Likewise you could do something similar with Areas. i.e. If you are filtering to just show one Area that when you create a new task using Tab+N, that the new task is created in that Area.
- When you are working thinking about a particular subject, i.e. you are working within a particular Area and/or Tag, surely that is the most likely time for you to come up with new tasks in that Area.
- Either way removal of any incorrect Tags is a simple matter of clicking the "x" beside the tag - which is much easier than adding a tag.