The biggest piece of advice I have to offer if you are tackling this project is to MEASURE CAREFULLY! we measured, taped, and then had to measure again. That was not fun. Also, take care to make sure your lines a straight...the few extra minutes it takes will save you lots of re-do time later.
There are so many fun options for painting stripes, you can do contrasting colors, tone-on-tone, or for an even more subtle effect, try using a different finish of the same color paint like eggshell and semigloss. For my project, I just mixed some white into a leftover can of the original wall color until I came up with something I liked.
First you will want to measure the height of your wall and figure out how many stripes you want and how wide they should be. I went with nine 9" stripes. Tape them off (the sections you aren't painting should be much more narrow than the ones you are painting because your tape will overlap into that section. After you tape, recheck your measurements and use a level to make sure your lines are straight. If you have the original wall color (your your base color) paint it lightly over your tape line, this way if any paint bleeds under the tape, it will match the original color and won't be noticeable.
Let the paint dry for a couple hours but not overnight. I have learned - the hard way- that you should take tape off, carefully, when it is just barely still wet. If you let the tape dry overnight it is more likely to pull up the paint underneath.
And there you have it! Easy horizontal striped walls! Now all you have left to do it decorate them! I hung one of our favorite wedding pictures along with two vacation photos I took during our last trip to Mexico!