1. You actually do need a desk. I am writing on my lap right now and both me and the computer are very warm.
2. You must have a routine. You cannot write whenever the muse dictates, because if you do wait, you will never finish any task.
3. You will have to exercise your imagination. I find youtube frankly very helpful. As I am writing about the winter of 1943 I can actually find things on yourtube that can stimulate my thinking.
4. You have to have clear goals and write a certain amount every day and always keep your eye on the prize.
5. Forget about a social life. You better like your own company. We all have a story in us, but only a select few can actually have the discipline to write a novel or other type of writing.
6. Constantly get readers to review what you have written and do not be afraid to adapt their comments. One way might even be to have a readers' club use your draft as one of their works