How do I plan my lessons? Well, it goes something like this:
1.) At the beginning of the year I identified the topics that I wanted to teach and when I wanted to teach them. I worked out a syllabus with plans for where the major projects would go and came up with some general ideas for how I wanted to present certain aspects of the material.
2.) The actual lessons then got put together at more-or-less the last minute. Usually I'd be working until 10 or 11 the night before, writing out lab worksheets or putting together slides. Then the next day I'd have to do it all over again.
3.) Eventually I started coming up with some multi-day assignments that would save me from having to start again from scratch every night. I also brought in La Clinica to do a two-week sex ed program, which took up an hour of class every day and thus cut the amount of time I had to plan activities for in half. This probably saved my sanity when I was trying to catch up on grading for the mid-semester marking period.
4.) Currently I have the students working on a big mid-semester Public Health Project, which is taking up good-sized chunks of time with comparatively little direct instruction on my part. Again, this has saved my sanity. Gustavo and I are team-teaching this section, since he knows the computers and the community far better than I; together we broke down the PHP into small, digestible steps for each day's activities. This has greatly reduced the amount of last-minute planning that I need to do ... though Victoria and I were still working on scaffolding the whole idea of a Public Service Announcement on the morning that the project began. :)
In general, then, I would say that I tend to plan the Big Picture far in advance and do the details at the last minute. This works better at some times than others; I feel like I'm pretty good at coming up with ideas to present material -- something that several others have echoed -- but it's easy for me to get to that point where I feel overwhelmed by all the stuff on my plate.
On the bright side, I think that the second unit of this class was structured in advance much more than the first unit. On the other hand, we're running about a week and a half behind schedule, so some of the stuff I had in mind for Unit 2 isn't going to happen. Figuring out what to keep and what to toss is the next big challenge.