In general, you should have a good and clear mind before smoking. Having said that, it's not always so cut and dry. I think you have to examine your intentions as to why it is that you're smoking. Are you smoking so that the drug will alleviate your depression? Let's try and tackle this analytically. It may go well. DMT can defy expectation and inexplicably generate euphoria even with the odds stacked against you. Having said that, you must realize that being depressed, the odds will be stacked against you, and it could go really badly.
Perhaps you're not merely looking to alleviate the depression, and are perhaps trying to get better insight into the roots of your problems and what (if anything) you may be able to do in your every day life to go about remedying the situation. Once again, this could go well, but it can also be extremely trying. You just have to know when you're going in ahead of time that it could be a rough session, but in this case necessarily rough. It needs to shake you out of your boots in order for you to be able to garner a new perspective on the situation.
I was stuck in a similar dilemma a couple days ago (and even now as it turns out). Two days ago, my 11 year old dog who led a good, long happy life was diagnosed with multiple metastasized tumors, she had an infection and her whole system was shutting down. We were told she wouldn't make it through the weekend. I was contemplating taking harmalas and DMT to see if I could perhaps spiritually help her in any way possible, perhaps with entity help or what not. In any case, I never got the chance, but I also don't know if I would have brought myself to take it anyway. Had to take her to the emergency animal hospital that night to put her to sleep because she couldn't wait any longer. I don't think I've actually experienced genuine sadness in over 3 years. Usually it's mild frustration or anxiety if anything, but this was the first time in a long time where I experienced true grief. I've been more shaken up over this incident than the passing of a number of close relatives. In any case, I've been thinking about smoking DMT over these past couple days. I'm not quite sure what I'm expecting to happen, and I fully understand that if I do decide to smoke that things could go completely and utterly awry. Having said that, I also believe that an experience under grief (a psychedelic experience of which the likes I've never even had the opportunity to explore) could come with some valuable lessons, even if the terms of the experience are rather harsh. So like you, I'm weighing all the pros and cons. In any case, I wish you the best of luck.