One method per question type. The AceUCAT method for Decision Making, step by step.
Decision Making is the most 'learnable' section — each question type has a clean method, and once you drill the method the question becomes mechanical. The time per question is generous compared with the rest of the test, so accuracy is everything.
Draw the smallest, most cautious diagram the statements allow, then test each conclusion against it. A conclusion only follows if it must be true in every valid diagram — default to 'does not follow' unless it is forced.
Convert the clues into a small table or ordering and apply them one at a time, starting with the most restrictive clue. Don't hold it in your head — write it down.
Place the numbers from the outside in: fill the most-overlapping region the data fixes first, then work outward so each region is counted once.
Decide whether events are combined with AND (multiply) or OR (add), convert everything to the same form (fraction, decimal or percentage), and watch for 'at least one' — it's usually easier as 1 − P(none).
The strongest argument is relevant and addresses both the problem and a workable solution. Reject arguments that are true but irrelevant, or that only restate the question.
An assumption is the unstated link the argument needs to stand. Negate the option — if the argument collapses, it was a required assumption.
For Yes/No statement sets, judge each statement on its own — they're scored together but reasoned separately.
Don't over-draw. The minimal diagram that fits the statements is the safest one.
Use the on-screen tools, but a quick sketch on the noteboard is usually faster.