When you're the host of a mission, every other player who joins your mission start next to you at the spot where you were standing when you accepted the mission. So please, PLEASE stop starting missions on the opposite side of the map, forcing everyone to drive 5 miles to get to the starting point.
When you look at the job list in your phone, it says how far away the mission is.
Invite to Gassed Up (2325m) (1 to 4 Players)
Usually, if you click on it and actually bother reading the text you'll see something along the lines of:
"First exchange is happening at the Los Santos State Gas Company in Cypress Flats."
Now you simply drive somewhat closer to Cypress Flats before starting the mission. No one is saying you have to be right on top of the mission marker before starting it, but no one wants to spend half of the mission driving to it from the middle of the wilderness. Please be more considerate of other players.