First off--I'm a lawyer, not a designer! So while I have some ideas about what I want, you're the expert in this space; don't be afraid to let your creative juices flow.
I picked my firm name, H.D. John, to satisfy the standard that law firms be named after the lawyers within them. I would like the H, the D, and the John to not just be written out in a line so they look like a boring name but to intersect in some way, so that they form some sort of a cohesive symbol/unit. Perhaps making the initials a bit vertical--the only example I can think of is BLG, http://www.blgcanada.com. Maybe try arranging the H, D, and John in a triangle or inverted triangle with the H and D slighty superimposed over the John?
The tag line underneath the symbol should be Enterprise Law, perhaps (but not necessarily) in italics. I may change this tag line over time if the identity of my firm changes, but I would like keep the H.D. John logo consistent for as long as I can to build brand recognition. I picked initials and my last name instead of my full name so I could build a brand with recognition beyond my own personal name like JWT, KPMG, etc. I may one day nix the John and re-brand as HDJ, so if the "J" were more prominent than the "ohn" (so the eye picks up "H D J") that might be helpful for future branding.
In terms of color, I was thinking of a maximum of 2 colors, drawing from red, blue, black, white and green, but I am open to other colors/ideas if you think they work. I'm alright with adding additional symbols/design to the words if it is not too busy.
Thank you, I'm excited to see your designs!