Resistance is any thought (or belief) that is in the way of you living the life you want to live. When you are not living the life you want to live, you can be sure there is resistance in you to your good. All of these thoughts and beliefs are tappable with EFT.
How do we find these resistant thoughts? The personal peace procedure by Gary Craig, found on http://www.emofree.com is an excellent way to find thoughts and beliefs that are creating resistance to our success, peace and happiness. Tapping on these core beliefs will dissolve any resistance you may have. Feeling 'deserving' is probably one of the most common resistant thoughts we have. Other common resistant thoughts are not being good enough (i.e. bad) and a sense of not belonging.
Another thought on resistance that Wayne Dyer makes is: Any thought that is not in alignment with the seven faces of intention (Creativity, Kindness, Love, Beauty, Expansion, Abundance and Receptivity) is a resistant thought.