As explained elsewhere, VV and LV were actually two separate, non-related series when they originally ran in Japan.  WEP did some "creative" editing in both series in order to create a unified series.  Below is a listing of some of those elements that connect LV and VV.

• The most obvious link is Galaxy Garrison (originally only in Dairugger XV; Earth was destroyed in Golion).  Both Voltrons fight for the Galaxy Alliance, of which planet Arus is a member.  Space Marshall Graham, Commodore Steele, and other GG officials appear in both series when either VF gets into situations requiring a decision from GG.  All GG scenes in LV were originally taken from D-XV.

• Planet Doom is a part of the larger Drule Empire.  Hazar, Nerok, Mongo, and other Drules make a few appearances near the end of LV Season 1.  They debate over whether they've given Zarkon too much autonomy.  In fact, the Empire was responsible for overthrowing Zarkon and putting Lotor on the throne in "Lotor the King" (LV ep 51).  Also in that ep, Lotor proclaims himself "King of the Drule Empire."  (Somehow I suspect Emperor Zeppo might take issue with that. :)

• Conversely, planet Doom is mentioned a few times in VV.  Hazar talks about sending the VV force to the slave dungeons on Planet Doom in "Help not wanted" (VV ep 7, which is on WEP's video "The Explorer Trilogy", a. k. a. "A new vehicle world").  And in "A temporary truce" (ep 11) we learn that Shannon's brother is a prisoner on Doom.
  
  
• Pidge, the young pilot of Green Lion, and Chip, who pilots Air Team vehicle #4, are twin brothers.  In the final episode of Season 1 ("Final Victory", LV ep 52), Pidge writes a letter to Chip to tell him that they've defeated planet Doom.  The VV Force has a brief cameo in the final scene when Chip reads Pidge's letter.  Also, in "Letters from Home" Chip becomes worried when he doesn't hear from Pidge.  He finally gets a letter at the end of the ep.  As Chip reads the letter, Allura, Pidge, the space mice, and LV himself appear in a flashback sequence.  The letter-reading scenes in this ep were also used in "Final Victory."  Also, in "A very short vacation" (ep 9) as they scope out planet Nanos for a rest stop, Ginger mentions that Pidge visited the planet once.
  
  
• In "Fleet of Doom", Zarkon and Throk join forces to attack the Alliance.  FoD also shows via flashbacks that the LV and VV forces (except Princess Allura, of course) all trained together at the Alliance academy.
  
  
• The original Lion Votron Force (Keith, Lance, Pidge, Sven, Hunk) apparently were the VV Air Team before being assigned to Arus.  Check "Space Explorers Captured" (LV ep 1):  The team is referred to more than once as the "Air Unit."  Also, Keith and Hunk are both wearing Air Team suits in their very first appearances!  (Yeah, I know; it's really Jeff and Rocky with Keith's and Hunk's voices dubbed over.  The scene was taken from VV ep 1, "In search of new worlds.")