Spend 24 hours consciously practicing your chosen Yama or Niyama or some aspect of it.
Practice ahimsa by not eating meat for the day.
Practice santosha by not complaining about work, your husband, or the weather.
Practice satya by not exaggerating. ("I'm starving!" or "I hit a million red lights on the way here!")
Practice asteya by not making personal calls, surfing the net or texting on business time.
Practice tapas by going on a one day "media fast", turning off the tv, radio, and internet gossip.
Practice saucha and aparigraha at the same time by finally cleaning out the basement or the back closet and donating the clothes you're not wearing to someone else who can!
Get it? It's challenging, but really fun!
If you find it helpful, jot notes down during the day about how it's going. Maybe make a note every few hours about whether or not you were able to keep your committment to yourself during that time.
Don't get discouraged - keep going!
At the end of the 24 hours write approximately 1/2 to 1 page summary of the experience. Please bring a copy to class with you and be prepared for a group discussion.
Your best bet is to choose one and begin right now!
Otherwise, the tendency is to "forget" indefinitely, or to make some small transgression of your committment and give up or start over with the illusion that getting it "right" and doing it "perfectly" is what will make your experiment and your Yoga "successful".
Please recall that this is a practice and each "mistake" helps us to grow in awareness. In that sense, there is no such thing as a mistake. Each lapse in awareness allows us to see ourselves more clearly.
Be warned: Sometimes in the process of cleaning the mind we "kick up some dirt", but it's so worth the effort!