Brian Stableford: True science fiction [is] fiction which attempts to build logically coherent imaginary worlds based on premises licensed by the world-view of contemporary science. (very slight editing from his GOH speech, ConFuse 91)

First step: Know your science. Learn astronomy.

--Read a book.

When I asked Larry Niven how he managed to get almost all the astronomy right in his books (since his degree is in math), he said he got up, walked over to a bookshelf, pulled out an astronomy textbook, opened it and read it. He said it with exaggerated simplicity. (We didn’t mention Ringworld.)

Some recently published astronomy books.

To accompany his triple astronomy book set, Voyages (To the Planets, Through the Universe, To the Stars, Fraknoi, Morrison, Wolff, 2nd edition, 2000), astronomer Andy Fraknoi has put up on the web a list of science fiction stories with good science (chapter by chapter). With comments on the stories. An eye-opener.

Space Station Science by Marianne Dyson (Scholastic, Inc.), winner of the Golden Kite Award given by the Society of Children's Book Writers and Illustrators (SCBWI) for the Best Non-fiction Children’s Book of 1999.
Web page for children’s science fiction activity in tandem with the book:

No Limits, Developing Scientific Literacy Using Science Fiction by Julie Czerneda (1999 Trifolium Books Inc.) Non-fiction for teachers, grades 8 - 12. Non-fiction for writers.

--Take a class.

Check your nearby community college  for an astronomy course schedule. A basic astronomy class would do, but larger universities have specialty classes, for example, a "Physics and SF" course has been taught at the University of Pittsburgh by professors Martin Vincent, David Snoke and Al Janis. Some university classes have web notes (like mine: Stonehenge to Hubble, Astronomy 88 and Stars, Planets and Galaxies, Astronomy 89).

--Ask experts.

All university professors set aside a certain amount of time each week to answer questions from the community (not necessarily from their students). It is part of their job description. Feel free to ask a science question (call, write or email) of any professor at any university . Believe me, people do it all the time. Persistence is the key--you may have to try a couple of people before finding one who is in town and not too busy when you approach them.

Ask the Space Scientist is astronomer Dr. Sten Odenwald's website. More Ask the Astronomer sites.

--Join a club.

I’ll use the example of Pittsburgh, but astronomy clubs are scattered throughout the world. The Amateur Astronomers Association of Pittsburgh (AAAP) has more than 600 members, holds star parties every month, sponsors talks in area bookstores, meets once a month at the Allegheny Observatory and runs contests for observing, photography and artwork. Members of the club also answer astronomy questions posed by the public.

--Research the web.

Astronomy resources on the web are extant. Some of the best are associated with:

-- Physlink.com's list of directories in Astronomy, including universities.
-- Observatories
-- Star Trek (go figure) The Science in Science Fiction
-- Planetaria and science museums: The Franklin Institute Science Museum in Philadelphia, The Exploratorium in San Fransisco

Note: Do not under any circumstances read Bud Sparhawk’s articles on dark matter and the expansion of the universe; they bring up a whole other issue about whether or not you can believe anything you read on the web.

--Read a magazine.

Recommendations:

Analog Science Fiction and Fact
Asimov’s Magazine
Artemis Magazine (on lunar development)
AstronomyMagazine
Sky and Telescope Magazine
Amateur Astronomy Magazine