I noticed in the Nexian DMT Handbook:

It may also behoove the user to seek out a more experienced sitter for guidance and support. Often this is unavailable, and as such, it would be more advisable for the user to perform the rite in solitude. An inexperienced sitter may inadvertently induce anxiety in the user out of negligence or unnecessary concern

I don't know anyone who has any experience with DMT or other psychedelics, so would you recommend I not use a sitter?

Or can anyone recommend a set of guidelines/advice to give to a close friend, albeit inexperienced, so they could be an effective sitter?

If you go ahead with not using a sitter, make sure things are nice and safe, no glass tables, no lit candle and make sure you sit propped up in a comfy chair/couch.

If you do have a sitter that isnt experinced with DMT, then they could be given the following guideline:

EVERYTHING WILL BE OK, no matter what they hear you saying, if anything, they must remain calm and reasure you that everything will be ok and this will be over in soon.
They should not try and communicate with you or ask you any questions while you are traveling unless needed.
They must not touch you unless asked to.

You should be fine on your own though, and if you doubt it, read above

Gamma is right in what he said.

Also, do check this FAQ question, might be of use.

While personally I havent heard many (or any?) story of people moving about dangerously sleep-walking like we hear with salvia stories,, only seen people making funny sounds and rolling around the bed a bit, I dont discount the possibility that it might happen for some unknown reason with a few rare people. And before you have smoked it at least once, you just dont know how you will react with it, so to be prudent, its better for first time to have someone that can restrain you in case you are going to walk out the room unaware of anything (though I find that highly unlikely).

If you dont follow the advice of at least for the first time having someone, then do make sure it is as good safe setting as possible, as the link above says.

If you do have a sitter, as gamma said tell him it will pass, for him not to freak out if you speak nonsense or look weird during it, the only thing he should do is stay quiet and patient for the next 5-30 mins (you, who are smoking, has to be the one to break the silence and start a conversation), and restrain you in case you stand up and sleep-walk dangerously.

Good luck and post back if you do it either way.