Spend more time reading in science topics. There are many popular science periodicals, e,g. Discover, Scientific American, etc. There are also many interesting books on science topics written for the general reader. (Textbooks often are poorly written and uninteresting.)
TIME magazine is OK, but its articles are shorter, simpler, less in-depth than when I read it as a kid: It's been dumbed down over the years. Spend more time reading other publications, e.g., Atlantic, New Republic, Harpers, etc.
Online, read blogs like "Arts & Letters Daily".
Stretch your abilities by reading just above your current level. Your public library or a large bookstore like Borders will offer a good selection of periodicals you can check.
Try to summarize, explain, and paraphrase what you've read---both orally and in writing.
Working on your vocabulary can help your comprehension too. Don't just pass over words you don't understand. Get into the habit of looking them up in the dictionary.
For writing, master the rules in "Elements of Style". Also read, "The Lively Art of Writing" and Zinnser's, "On Writing Well". Do brief practice essays and get feedback from people that write well. Then revise. Clear thinking, practice, and revision are important in developing your writing skills.
You learn to read and write well by reading and writing. In the past, people learned to write well by consciously imitating the style of good writers. Obviously, you don't necessarily want to imitate the styles of the 18th and 19th century, but studying the style and structure of good, clear contemporary writers can be helpful. Anthologies of essays may contain some good examples.
I hope these suggstions are of some help.