There are some fantastic books on the market for creating animation in general. One in particular I strongly recommend picking up is
The Animator's Survival Kit by Richard Williams (the lead animator for
Who Framed Roger Rabbit). Not only does it cover common techniques in great detail, it's also an entertaining read.
Other books you may want to look into are ones that cover things like artistic theory (perspective, color, the human form, etc...) and story development.
One title I've relied upon for basic story telling techniques is
Inspired 3D Short Film Production by Jeremy Cantor and Pepe Valencia. While you may not be working in 3D, much of what it covers remains perfectly valid even with apps like Moho or Flash.
Once you have a good grip on the basics, you can start looking for books covering certain programs and animation/art styles. There are literally thousands of titles you could use to assist you in your work.
Also, keep in mind, nothing beats the old method of using a piece of paper and a pencil for brainstorming and character/story creation. After all, you can't create quality animation without a plan to hold it all together.
Finally, be prepared to spend a lot of time doing simple trial and error. It usually takes several years for most animators to master their techniques. If you look at the people in the animation industry that have built a reputation for themselves, you'll notice the majority of them are in their 30's and 40's. Needless to say, don't expect to become good at it right off the bat.
Above all else, just be sure to take the time to enjoy what you're doing. If you don't enjoy the work involved, it becomes a pointless endeavor.
