I think a very good practice is to, of course, work on the assignment a few days before it is due. I am sure that you will here that one a lot, but there is a variation on it. See most people will not feel like they have the time to do any significant work on an assignment until the night before it is due, and this may be the case, but I would at least recommend to look at the problems for a few minutes. Just read through them and start thinking about them. I find that this works quite well, because I can be thinking about a problem when I am not even sitting down doing work, like while I walk to class or stand in line at Platt. That time can be enough to figure out things that you do not know how to do and then go and ask the prof about those problems specifically. This type of tactic can be used for anything from regular homework problems, to essays assigned in a hum class.
I believe that a good practice is to not work on one thing, or one subject for a very large block of time, say more than 2 hours or so, and have another piece of homework to spend some time on and take a break from the major piece of work. I find that I am actually much more productive when I come back to it than I was when I was working straight on it. Now this does not mean to switch around every 5 minutes, but a couple hours is enough time to get into the subject without getting bogged down.
I think that the last thing that I am going to suggest is something that you may not hear too often, and feel free not to use it if you do not agree, or whatever. I think that it is very important to have something that is totally different than work that you can use as a relaxation/distraction when you have a lot of work over the period of a week. I like to mountain bike a lot, and so what I do, honestly, is train. If I have a week that is going to be really busy, I do all that I can to bike an extra amount that week, and I honestly feel better, and feel that I do better in the work that I have to complete than if I had not biked. I have tried a few tests with this and it really seems to work. I think that it is really important to get your mind off what you are doing and relax it for a while, so that it will be maximally efficient for more time. Burn out is a all too common thing around here, and I think that it is because people just work themselves to death, when they would be a lot more successful if they just took some quality breaks.