I find that I have trouble writing if I'm not at least partially in the right mood. That means being relaxed, not too stressed over real life issues, and willing to be open to new ideas as they come in.
Usually when I sit down to write I'll reread the existing manuscript for at least a few pages leading in to where I'm writing. If I don't do this, I find that I have trouble keeping the same tone that has been established for the book so far. Every few writing sessions I'll go through and reread the whole thing, making small edits and consistency updates along the way. Obviously these full rereads happen less often as the manuscript grows, but they should be happening now and then all the way up until it's finished. This really makes a difference for me in making sure that I don't have problems with some detail established early on that becomes more important later in the story. I also have learned to be willing to revise existing sections - sometimes extensively - to insert a detail like this when I realize that I really needed to establish something earlier in the story.
I normally write for 1 to 2 hours at a time. In general I find that I put down approximately 2,000 words in an hour, give or take a few. This is the equivalent of typing 33 words per minute (wpm) for 60 minutes (or more) straight. In reality, it means that I'm writing in bursts of 60-70 wpm, then taking a bit to revise what I just put down or think about the next passage. There's some short breaks in that hour as well. Sometimes it goes faster, sometimes slower - you never know until it's done.
I use an HP laptop that I also use for playing games and watching movies occasionally. It's big for a laptop - I can't type effectively on anything that's less than a full-sized keyboard, thanks to my finger size - but I like being able to pick it up and move to a more comfortable place on the couch, or head out camping, or whatever when it feels right to do so.
The downside to typing on a laptop is that it's definitely less ergonomic. I have a lap bench thing I use at home, but there's no cushions for my wrists and I make sure to take frequent breaks to stretch my arms and make sure I'm not stiffening them up too much. Even so, a well set up desk would be a better setup, and at some point if I get published and move towards doing this long-term I'll probably move back to my desktop for writing when I'm at home.