The original Guardians of the Galaxy, the Martians of H.G. Wells and Killraven, Warrior of the Worlds!

Note that items on this Reading Order are placed in chronological order for Earth 691, which does not always match where events crossover with Earth 616, the main Marvel Universe.

The War of the Worlds
The original novel by H.G. Wells is canonical on Earth 691, taking place in 1901.
Essential Killraven, vol.1
Reprints Amazing Adventures #18-39 (May 1973 – December 1976); Marvel Team-Up #45 (May 1976); Marvel Graphic Novel #7 (August 1983) & Killraven #1 (February 2001).
The bulk of this volume takes place in the alternate future of Earth 691, but the Marvel Team-Up story crosses over with the Marvel Universe.
Wolverine & the Black Cat: Claws II
Reprints Wolverine & Black Cat: Claws II #1-3 (August 2011 – November 2011).
Wisdom: Rudiments of Wisdom
Reprints Wisdom #1-6 (January 2007 – July 2007).
Marvel Zombies 5
Reprints Marvel Zombies 5 #1-5 (June 2010 – September 2010).
It is unclear whether the Earth-691 visited in this storyline is the actual one, or just a closely related alternate. This story crosses over with the main Marvel Universe.
Guardians of the Galaxy: Tomorrow’s Avengers, vol.1
Reprints Marvel Super-Heroes #18 (January 1969); Marvel Two-In-One #4-5 (July 1974 – September 1974); Giant-Size Defenders #5 (July 1975); Defenders #26-29 (August 1975 – November 1975); & Marvel Presents #3-12 (February 1976 – August 1977).
Guardians of the Galaxy: Tomorrow’s Avengers, vol.2
Reprints Thor Annual 6 (1977); Avengers #167-168 & 170-177 (January 1978 – February 1978 & April 1978 – November 1978); Ms. Marvel #23 (April 1979); Marvel Team-Up #86 (October 1979); Marvel Two-In-One #61-63 & 69 (March 1980 – May 1980 & November 1980).
JLA/Avengers: The Collector’s Edition
Reprints JLA/Avengers #1-4 (September 2003 – December 2003).
The Guardians of the Galaxy appear among the Avengers in this story, drawn from approximately this point in their timeline.
Guardians of the Galaxy by Jim Valentino, vol.1
Reprints Guardians of the Galaxy #1-7 (June 1990 – December 1990) & Annual #1 (July 1991); Fantastic Four Annual #24 (July 1991); Thor Annual #16 (July 1991); & Silver Surfer Annual #4 (July 1991).
Crosses over with the main Marvel Universe.
Fantastic Four: Korvac Quest
Reprints Fantastic Four Annual #24 (July 1991); Thor Annual #16 (July 1991); Silver Surfer Annual #4 (July 1991); & Guardians of the Galaxy Annual #1 (July 1991).
Crosses over with the main Marvel Universe.
Guardians of the Galaxy by Jim Valentino, vol.2
Reprints Guardians of the Galaxy #8-20 (February 1991 – January 1992).
Guardians of the Galaxy by Jim Valentino, vol.3
Reprints Guardians of the Galaxy #21-29 (February 1992 – October 1992) & Annual #2 (1992); & Marvel Super-Heroes #18 (January 1969, Guardians story only).
Guardians of the Galaxy Classic: In the Year 3000, vol.1
Reprints Guardians of the Galaxy #30-39 (November 1992 – August 1993) & Annual #3 (1993); & Marvel Comics Presents #134 (August 1993, Major Victory story only).
Guardians of the Galaxy Classic: In the Year 3000, vol.2
Reprints Guardians of the Galaxy #40-50 (September 1993 – July 1994) & Annual #4 (1994); & Galactic Guardians #1-4 (July 1994 – October 1994).
Thor Corps
Reprints Thor Corps #1-4 (September 1993 – December 1993); & Thor #337, 384, 433 & parts of 438-441 (November 1983, October 1987, June 1991 & November 1991 – December 1991).
Takes place during In The Year 3000 at some point after Guardians of the Galaxy #43; also crosses over with Earth 8710 and the main Marvel Universe.
Guardians of the Galaxy Classic: In the Year 3000, vol.3
Reprints Guardians of the Galaxy #51-62 (August 1994 – July 1995) & Annual #4 (1994).
Guardians of the Galaxy, vol.1: Legacy
Reprints Guardians of the Galaxy #1-6 (July 2008 – December 2008).
This volume takes place in the modern day of the Marvel Universe, but includes important appearances by Earth 691 characters.
Guardians of the Galaxy, vol.2: War of Kings, Book 1
Reprints Guardians of the Galaxy #7-12 (January 2009 – May 2009).
This volume takes place in the modern day of the Marvel Universe, but includes important appearances by Earth 691 characters.
Guardians of the Galaxy, vol.3: War of Kings, Book 2
Reprints Guardians of the Galaxy #13-19 (June 2009 – December 2009).
This volume takes place in the modern day of the Marvel Universe, but includes important appearances by Earth 691 characters.
Guardians of the Galaxy, vol.4: Realm of Kings
Reprints Guardians of the Galaxy #20-25 (January 2010 – June 2010).
This volume takes place in the modern day of the Marvel Universe, but includes important appearances by Earth 691 characters.
Guardians 3000, vol.1: Time After Time
Reprints Guardians 3000 #1-5 (December 2014 – April 2015).
Korvac Saga: Warzones!
Reprints Guardians 3000 #6-8 (May 2015 – July 2015); & Korvac Saga #1-4 (August 2015 – November 2015).
Guardians of the Galaxy: Tales of the Cosmos
Reprints Guardians of Infinity #1-8 (February 2016 – September 2016; lead stories only).