The first step was that I wrote an email about every idea I had. I had to get them out of my head and on to the page before I could let go of them and get back to what I was doing. So, I emailed them to her with the subtitle of "Bin: XXX". Bin meant that we met every couple of weeks and reviewed the dozens of ideas - keep, shelve, reprioritize, what action did I take? I did that with every single email.
Then I got to the point where I kept my own list on the computer. Now, in a giant step backward technology-wise, I carry a journal that i write them in. Each week I readdress the ideas.
I have to get them out of my head, or I can't move forward. But, I don't want to get off point from what I'm working on.
Interesting side note - I find that when I'm doing something creative (mind mapping in particular) that I start generating more and more ideas. However if I'm doing something more mechanical, my mind doesn't wander so much.