ACT Reading and ACT Science both rely heavily upon reading comprehension, but they also require you to budget your time well. If I had to give one tip for improving both your ACT Reading and Science scores (without knowing any more details about your strengths/weaknesses), it would be to work on the way you read the passages.
In ACT Reading, this means not getting too caught up in reading and understanding every single bit of every single passage - you only get points for the questions you answer, after all, not for the passages you read. When you're doing practice tests, make sure you monitor your time, and keep track of where you're spending too much time. There are more in-depth tips on how to avoid running out of time on ACT Reading in this article.
You might be surprised to learn that ACT Science is actually way more about reading comprehension than it is about scientific knowledge. In fact, on ACT Science it's even more important than it is with ACT Reading that you make sure you're not getting so caught up in the passages that you run out of time to answer the questions. One of the most effective ways to approach ACT Science, actually, is to skip the passages altogether and head straight for the questions. If you're not comfortable doing this, skimming can work as well. Again, we have more information about this in our article on the best strategies for reading the passage on ACT Science.
Finally, our ultimate guides to ACT Reading and ACT Science contain a bunch more links to free strategies and advice you can use in your studying.
I'd also add this one final note: ACT English and Math may actually predict college success better than your ACT Composite score (which includes Reading and Science), so don't judge yourself too harshly for doing poorly on those two sections. As this article from our blog states, judging your own future potential for success based solely on your test scores is likely to yield inaccurate results.