Both are school comedies in a 4-koma format.
Very similar humor and the inspiration from Azumanga Daioh is very clear in Nichijou.
Nichijou is far more episodic and has some sci-fi elements, but the overall feel is the same.
Both of these manga focus on the lives of high school girls and their ordinary day to day life. Except their life isn't really all that ordinary, crazy stuff happens all the time. Nichijou cranks the absurdity factor up by ten and presents you with a much wilder ride but the base premise is still there. Both still have lovable characters and both will give you a fun time.
If you're looking for something equally as light-hearted, I recommend Nichijou: there's more comedy and it gets a little weird at times, but like Yotsubato!?, all of the characters are lovable, and you can pick it up at any point due to a lack of 'plot' - each new chapter brings a new story.
Both of these titles are standalone slice-of-life narratives that depict, in an extraordinary and exaggerated manner, the daily lives of highschoolers. Moreover, both titles share very similar narrative styles; particularly in regard to how comedy is achieved.