You can make a field required in the form - that's probably the first option.
You can add validation rules, one per field, as you've said.
And that's about it.
The other approach is to put conditional formatting on the submit button, so that it is disabled until all fields are not blank.
You can add labels using the Text option in a Calculated Value, and this allows you to show/hide the labels as desired using conditional formatting.
Hope this helps!