Question
I am building a fence on a lot which has a slope. Now normally I would just step the fence down every post or so but the neighbourhood all have fence's with a gradual slope. By this I mean all the 1x6's are cut at an angle, what is the best way to achieve this effect

Answer
You install the fence post first then the top, bottom and middle rails. Then using a level you attach the pickets. Check every fourth of fifth picket for level and adjust as necessary. A minor gap here or there will not be noticeable if you keep this check regular. If your slope is fairly even you can use a string and pull it across the tops of the pickets from one corner to the next or from one point of significant grade change to the next (going post to post) and then snap a chalk line at he top and cut all the pickets off along the chalk line for a straight sloped look.
Or you can simply use a block of wood along the ground 2" thick and set each picket on the wood as you move across the slope (move block wood to each new picket). This look makes the fence undulate with the surface of the ground bellow it. For a more consistent look use a longer block and set several pickets each time you move the block. Be sure when you move the block you overlp the last position. This keeps pickets more even.

Most home stores have cheap paperback picture-how to books that show illustrations on this.
Or try googling "sloped fence"
Here is an excellent link:
http://www.bobvila.com/BVTV/Bob_Vila/Video-0215-01-1.html