I try to place spawns out of line of sight.
I start from the base and move away as I place them, placing the furthest ones last, but all in one session.  Then I place the other team spawns.
I have noticed that if I add spawns to a map after I have placed other items or even published it, that you tend to spawn in the last ones placed first.  Then all goes back to the normal, closest to base, but furthest from enemy.