I used this to preview the most simple two frame animations: http://www.moddb.com/downloads/sprite-sheet-player
Here’s great reference for looking at great sprite animations: http://www.spriters-resource.com/ and if you’re looking into creating more complex sprites with bones and keyframing, consider using Spine: http://esotericsoftware.com/
I am, by the way, a terrible animator by nature, due to a profound lack of experience with it and an equal lack of patience. Therefore I went with a very simple and rather quirky style for the game animations. I was originally going to put in more frames for the bat and owl animations, but when I tested the two-frame anims in the engine I was surprised that they actually fit the look.
I can’t stress how important it is to keep looking at things in-game, the lack of which I know I’ll regret (it’s pretty easy to forget when you’re happily bashing out drawings, but there’s nothing more annoying than having wasted half an hour on a frame that’s useless). Pretty similar to testing parallax backgrounds, or anything really!
I got pretty lucky with the skip, I think, mostly by looking at walk cycle reference on Google images and trying to interpolate something based on them.
I guess the number one thing I found that worked was simply checking them in the game over and over again (and also using the Sprite Sheet Player program to test them quickly). We don’t need more complex animations right now due to the fun and eclectic look we’ve established so far — hence my decision not to go with Spine. Having tested the demo version out, if I did have to create more complicated character animations I would switch to it; it is far superior to Flash, which crashes about once every 15 minutes for me…