I find that reading the question stem first works best for me, especially concerning timing. If I for some reason forget to do so, I always find myself having to go back and reread the stimulus again, which is a waste of time. My general strategy that I've found (from 7sage and the LSAT Trainer) is to:
1. Understand your task - read the question stem to trigger how to think about the question and decide whether you're reading for an argument or something else. 2. Evaluate the stimulus 3. Eliminate wrong answer choices (for most questions) - for some question types you will have a strong idea of what the answer choice is before looking at the options, but you should still eliminate wrong choices 4. Confirm the right answer - be sure not to compare two possible answers against one another, only compare them individually against the stimulus
Read the question stem first! To echo what @lbalestrieri stated, you need to read the question stem in order to figure out how to approach the question. Your task for an assumption question when compared to an inference question is going to be vastly different. The question stem is your guide to knowing how to read the stimulus correctly.
Comments
1. Understand your task - read the question stem to trigger how to think about the question and decide whether you're reading for an argument or something else.
2. Evaluate the stimulus
3. Eliminate wrong answer choices (for most questions) - for some question types you will have a strong idea of what the answer choice is before looking at the options, but you should still eliminate wrong choices
4. Confirm the right answer - be sure not to compare two possible answers against one another, only compare them individually against the stimulus
Hope this helps!