Here is a link to a great strategy guide that helped me http://www.orionsector.com/pages/galciv/downloads/The_Unofficial_GalCiv_Strategy_Guide_v1_0.pdf
There is a thread in the strategy part of the forum at the top by Frogboy called "Morale tips".
In addition to what Geoffrey said, you can also build planet improvements (like entertainment network), research tech (like virus elimination), and use the tax rate to influence morale. With a higher morale you can raise the tax rate to make more bc and you will grow your population faster. With a lower morale you may decrease planet growth and actually lose your planet to the I-League.
There is also an emergency morale boost under the "Details" section of the planet information that allows you to spend bc to boost propaganda and morale. Be careful though because it is easy to forget where you are spending that extra bc and the expenses add up.