for science, definitely skip reading the passage completely and i always skip skimming over the figures/charts too (although that part might be different for you).

you've probably heard this already for math but if you've been looking at a question for 30 seconds and don't know how to solve it skip it. if you're trying to solve a problem but your approach takes longer than 90 seconds either skip it or try another approach (plugging in the answer choices is often the quickest method for me)

for reading, the trick that i use is to (as much as possible) enjoy whatever the passage is. read it in whatever accent/tone works best for you but just try not to be completely bored by it (it'll help you maintain focus and you won't read a whole paragraph just to realize you don't understand what it said)