It is easy to get zero credit for certain problems in Calculus II,  if you omit the first step. Here are examples:

-- In preparing for Calculus I, fail to learn algebra and trigonometry.
-- In studying Calculus I, fail to learn substitution as a technique in antidifferentiating / integrating.

-- In substitution for an antiderivative, use the same letter for the new and the old variable.
-- In evaluating an improper integral, fail to define a family of proper integrals (prior to taking the limit).

-- In deciding convergence/divergence of series, ignore the partial sums and decide the convergence/divergence of terms.
-- Claim that the divergence test proves convergence.  (It cannot.)
-- Claim that the alternating series test proves conditional convergence.  (It cannot.)

-- In separation of variables, fail to separate variables.