I am very good at remembering dreams, and got good at it simply by writing down what i do remember.
Though i have no exp with dmt, this seems to work very well for dreams and i'm sure the skill of remembering could be developed the same way for dmt trips, as is my eventual plan
Get a journal, and to start with, just write down any and all details you can remember, the minute-est things , like colours or words. you may remember more later, write this down too.
The next time, do the same, and you will start to find that you can remember more and more details each time.
Obviously it's going to be harder to remember a dmt trip than a dream because of the time and speed, but i reckon definately writing stuff down goes a long way. You wouldn't remember a speech without writing it down. Plus, it would be fun to read back on previous trips, as it is for me reading back on dreams. I can read of one of my own dreams from say two years ago and while i'm reading, remember dreaming the whole dream in detail exactly as it was the first time.
Perhaps also just telling yourself / asking beforehand that you will remember as much detail as you can may be helpful.