State tax filing

Thank you both for quick answers.  You're on my wavelength about research first,  and I've done plenty, though just on paper.   The Kiplinger articles are great.   I am indeed a retiree.  I've narrowed my sights on the corner where three states meet and want to make sure I'm not missing anything.   NOT a math person and don't want to make a glaring mistake.   Any alternate ideas welcomed.