How do you practice mindfulness of thoughts?

[fopylo]

So I've been doing a bit of Leo's exercise to write down 50 thoughts for the next week (been writing about 30 now) and I've stumbled on some things.

When I have a thought which is more detailed I want to write it down and use it for my practice, but I'm not next to my journal. So I kinda try to hold on to this thought and feeling, and then by the time I get to my notebook it doesn't feel quite natural. I've subconsciously been suppressing other recurring thoughts in this time period, and also I am trying to recall an emotion I had a few moments ago, which is out of the present moment. Also when writing down the expression I have some images in my mind which I'm planning on describing, but as I'm writing the expression the images change and I didn't plan it and I still try and write the images I had, and then my mind hurts a bit from thinking and concentrating.

So what should I do? Should I just write right away as things flow? The problem is that I don't have detailed thoughts while next to the notebook, it usually happens when I'm busy doing something. It's almost as if recalling a memory (thought) is like trying to monitor the present thinking. I can't exactly write down the present stream of expression, content of thought, images and feelings all together, because as I'm starting with writing the expression then everything else I mentioned is starting to shift into other forms and then I get a written down description of something that never existed in the first place.
Oh and by the way, this exercise made me be in my head and less mindful than usual, it felt quite bad at the gym talking to people and I was in my head so much.

How do you go about it? I would like to hear