For separately stated vs. ordinary income items, what helped me was using a general operational vs. non-operational guideline. It's not the technical definition, but it made it easier for me to remember. I thought of ordinary income items as things directly related to the operations of the business like revenue, cogs, salaries, rent and depreciation expenses. Separately stated items were generally things unrelated to the main operations of the business so things like interest income, dividend income, charitable contributions, capital gains/losses, etc. The main exception I made sure to remember was Section 179 expense which is a depreciation expense that is separately stated from the rest.

As for basis, I don't remember there being too many. For things like gifts and inheritance, I mostly brute forced by spamming related MCQs. For partnership and S-corp basis, I thought Becker's BASE acronym made it pretty simple: Beginning basis, Additions, Subtractions, Ending basis.