In all honesty, I think the prepping part may have been harder than the painting part. There were three main things that we did to prep the house.
1) Power Wash
I don't have any pictures of the spray washing, as my faithful father took on this task, while my hubby and I worked our day jobs. The take away is that he used an electrical power washer to spray down both the house and the garage. He worked from top to bottom, and used just enough pressure to blast off the dirt, but not so much pressure that he blasted off the paint or shakes (our house has cedar shakes).
The Scrapping was a major undertaking. Again, my father started the process while we were at work, and we joined in on the "fun" on Friday afternoon. We used a combination of these things to get the job done.
Another Paint Scrapper
Good ol' fashioned flat head screwdriver.
We actually purchased all of the tools at Home Depot (with the exception of the screwdriver, which we already had). So, feel free to visit your local HD for everything you need.
Here is a pic of the front of the house post scrapping. We had to scrap not only the flat surfaces, but also along the bottom of the shakes, where older paint had built-up. It was crucial that we removed both built up paint and peeling paint, as moisture can build up there. Plus, if you don't knock-off that stuff, you risk it chipping off later and messing up your paint job.
The final prep was taping. We rented an industrial paint sprayer for the big day of painting and we knew that we didn't want paint splattered all over our nice, crisp white windows. So, we taped off each window and door, using plastic drop clothes and painters tape.