I think set and setting is a lot less important than on other psychedelics especially when compared to something like LSD.

Doing it with someone you trust in a good environment might help you continue further through the DMT Worlds because the more relaxed you feel, the easier you can "fall into" the experience. But i've always done it alone. Always when i tried to control the trip it backfired. Like "going in with intent" as in asking questions...just imagine the response of a "colorful god nebula" shrugging his shoulders...and then continuing with what should continue.

edit: I even smoked DMT while crying out of sadness. It did not influence the experience as far as i can tell. It's like these minor humanly things are nothing on the grand scheme of DMT.