When you have a big goal, do at least a little of it every day. Cory Doctorow writes books and stuff, and writes for at least twenty minutes every day. I write computer software, primarily Obnam, my backup program, and recently wrote the first rough draft of a manual for it, by writing at least a little every day. In about two months I got from nothng to something that is already useful to people.
I am now applying this to coding as well. Software development is famously an occupation that happens mostly in one's brain and where being in hack mode is crucial. Getting into hack mode takes time and a suitable, distraction-free environment.
I have found, however, that there are a lot of small, quick tasks that do not require a lot of concentration. Fixing wordings of error messages, making small, mechanical refactorings, confirming bugs by reproducing them and writing test cases to reproduce them, etc. I have foubd that if I've prepared for and planned such tasks properly, in the GTD planning phase, I can do such tasks even on trains and traun stations.
This is important. I commute to work and if I can spend the time I wait for a train, or on the train, productively, I can significant, real progress. But to achieve this I really do have to do the preparation beforehand. Th 9:46 train to work is much too noisy to do any real thinking in.