Thanks everyone for further advice here.
kaleidoscope eyes, if you're interested in learning about vipassana meditation, I can recommend a few resources that I think are quite excellent. On the progress-as-fast-as-possible side, we have
Mastering the Core Teachings of the Buddha. This book is completely devoted to the technical and practical aspects of insight and concentration meditations, done with clear goals in mind, and only delving into theory (never dogma) when it's relevant to the actual practice.
Coming from a similar perspective but with a higher focus on tranquility and less of a focus on intensely energetic practice is
Kenneth Folk's instructions on vipassana practice. This guy's advice is also great, though the two authors don't entirely agree on some aspects of meditation. What's clear is that either approach works, despite the differences. All of the information on his website under the heading "1st gear" in the navigation menu relates to concentration and insight meditation.
From the standpoint of Theravada Buddhist religion and dogma,
Practical Insight Meditation by the insight master Mahasi Sayadaw is one of the best. The instructions are as effective as the ones found in MCTB or at Kenneth's website, but I personally find Practical Insight Meditation deeply steeped in the Buddhist religion and therefore difficult to understand if one isn't fluent with the doctrine.
Back to DMT, I particularly like your advice, shoe! I don't know why on earth I hadn't thought of it myself, as I use the approach of cultivating love/compassion whenever I'm having a miserable time during meditation, and in fact the cultivation of love/compassion before I meditate will generally prevent the miserable time from happening in the first place.
I'm thinking I can try a period of lovingkindness meditation before DMT. In fact, if I can cultivate lovingkindness AND equanimity, that should be the optimal mix. Cultivating equanimity and mindfulness before blasting off has given good results before, though it does tend to make me go through the stages of insight meditation during trips. That can really suck if I end up tripping in an unpleasant stage! But lovingkindness and equanimity are the keys to getting through those experiences in meditation, and I don't see why DMT should be particularly different in that regard.
As for bodily health... I need to eat lots more food, and this habit I've just recently developed of getting fast food once or twice a day needs to go. I never used to eat fast food at all... Anyway, I'll probably live a long time because of my low calorie intake, but it isn't all fun and games to have such a small stomach! Aside from lacking middle- and upper-body strength and muscle mass, my body works pretty well. Perhaps an exercise routine would go a long way in improving general health, and I could see that having an effect on hyperspace experiences. DMT, it seems, forces you to face whatever is going on by turning up the gain on all your senses. If the body feels bad, you feel bad!