You may want to assure the validity of tool content by an expert, perform exploratory and confirmatory factor analysis, and correlate its scores with another valid tool. This is not a simple process. 

There have been a number of discussions here on this topic. Use the Search function for Questions to look up "validity scales" and "validity questionnaire."

I agree with David.

However, it depends what you are trying to do. For example, sometimes construct validity if most important (if you are measuring a concept); sometimes predictive or concurrent validity will suffice (if there is a criterion you have to predict).

Perhaps, you could find useful this article (see the link below) where we address step-by-step various types of validity in both qualitative phase (e.g., face validity, content validity and construct validity) and quantitative phase (e.g., convergent and discriminant validity) of constructing a research instrument.

This is the link to the paper:

https://www.researchgate.net/publication/299744463_How_to_Construct_and_Validate_a_Questionnaire_on_L2_Motivation

Please do not forget that establishing reliabity is also important. We discuss this in the article too.

Good luck!

Working Paper How to Construct and Validate a Questionnaire on L2 Motivation