Read the blurb - Read the little introductory blurb before Passage A even begins. This will help you understand the time period, the topic, and even the relationship between Passages A and B.
Read Passage A - If you incorporate a specific reading strategy to do that, great! If you don’t know what I’m talking about by “specific reading strategy,” then just read the passage like you would read anything else.
Answer “Passage A ONLY” Questions - While Passage A is fresh in your mind, skip to the first set of questions that are about Passage A only, and answer all of them. Finish this before moving on.
Answer “Passage B ONLY” Questions - Now skip to the second grouping of questions, and answer ALL of them! They will be about Passage B and only about Passage B, which is the passage you just read and have fresh in your mind!
Answer single-passage questions first - Answering questions about individual passages will often give you clues you can later use to answer questions that deal with both passages.
Guess on multi-passage questions - Figure out which type of question you tend to get wrong and then focus on improving that skill.
Use the process of elimination - If even just part of an answer is wrong, you can eliminate that answer choice immediately. There is only ever one unambiguously correct answer.
Practice with official SAT paired-passage questions - Since not many ACT paired-passage questions are available for practice, it's a good idea to use SAT paired-passage questions so you can get more used to answering questions that address multiple passages.