I think what you might want to do (this is what I like to do anyway) is go into Photoshop or something comparable and draw up your plan for what you want to do in it. Plant/wood/rock layout and everything. Do research on what plants you want and where you want them and just draw up a overview plan of what you are looking for. Then afterwards find what needs to be done to achieve that goal. It gives you an idea of the requirements and where you need the lights and such. Also let's you blueprint your tank.
I hate to say this Matt - but that's exactly the opposite of what I do. With my 45 I just jammed it full (mainly to fend off the algae from all the light) and then moved and moved, and pruned and replanted, etc, etc. Hell, I just trimmed and moved around a bit this weekend - ripped out some hairgrass, etc. I can't see it on a piece of paper - I have to jam the tank full and go from there. The patience required for the 150 to "grow in" may very well be a challenge for me - I'm psyching myself up for that right now!!